Microgrid system controller for creating and maintaining a microgrid

ABSTRACT

A microgrid system controller includes a regulated bus, a variable-frequency drive (VFD) inverter, a generator coupled to a rotatable flywheel, a resistive load; and a plurality of actuatable switches. The microgrid system controller may also include a battery and charge controller or a battery storage device. The plurality of actuatable switches couple some of the various components.

CROSS-REFERENCE TO RELATED APPLICATIONS

This applications claims priority to U.S. Provisional Application No.63/032,524, filed May 29, 2020, and U.S. Provisional Application No.63/109,301, filed Nov. 3, 2020, the contents of each of which areincorporated herein by reference in their entirety for all purposes.

BACKGROUND

Distributed energy generation is key to a resilient energy supply, butdistributed resources like solar power do not have any intrinsic surgecapability like that provided by the angular momentum of a generator.Without some form of dispatchable energy storage, power surges, e.g.,those produced when charging capacitors or starting or stopping a largemotor, cause voltage fluctuations that can disrupt or damage otherconnected equipment. Moreover, most solar inverters can only supplypower to a stable, well-regulated grid. As soon as the grid goes down, asolar array and conventional inverter turn off. This radically limitsthe effectiveness of solar power as an emergency or fail-safe powersource.

Battery storage systems can provide surge capacity. If a grid node suchas a residence is electrically disconnected from the power grid, e.g.,via a master service disconnect switch or breaker, a battery storagesystem can regulate a voltage waveform that allows a conventionalgrid-tied solar inverter to feed power into the isolated node. Atpresent, the cost of a battery storage system and its attendant powerelectronics may be excessive because electronics and magnetics may needto be sized for peak power, which may occur only for a second or twoperiodically through the day.

SUMMARY

Some embodiments described herein include novel microgrid systemcontrollers that provide alternative approaches to providing andabsorbing surge power and generating a high-quality, stable voltagewaveform, while obviating excessive battery storage andpower-electronics costs. Some embodiments comprise one or more of agenerator, a flywheel, a motor, a motor-controller, a power source, aload switch, a source switch, and an auxiliary load. Some embodimentsmay further comprise a switch to connect and disconnect from the grid orapparatus to report the connection state to the grid.

In accordance with an embodiment, a microgrid system controller includesa regulated bus; a battery and charge controller switchably coupled tothe regulated bus; a variable-frequency drive (VFD) inverter coupled tothe battery and charge controller; a generator physically coupled to arotatable flywheel and switchably coupled to the VFD inverter; aresistive load switchably coupled to the regulated bus; and a pluralityof actuatable switches. The plurality of actuatable switches include afirst actuatable switch configured to selectively couple a photovoltaic(PV) inverter to the regulated bus or to an external electrical panel; asecond actuatable switch configured to selectively couple the regulatedbus to the external electrical panel; a third actuatable switchconfigured to selectively couple the regulated bus to the battery andcharge controller; a fourth actuatable switch configured to selectivelycouple the VFD inverter to the regulated bus or to the generator; afifth actuatable switch configured to selectively couple the generatorto the external electrical panel; and a sixth actuatable switchconfigured to selectively couple the resistive load to the regulatedbus.

In an embodiment, wherein the plurality of actuatable switches comprisea seventh actuatable switch configured to selectively couple auser-configurable load to the regulated bus.

In another embodiment, where during a first state power from the PVinverter is supplied to the external electrical panel, the plurality ofactuatable switches are configured such that: the first actuatableswitch couples the PV inverter to the external electrical panel; thefourth actuatable switch couples the VFD inverter to the regulated bus;and the sixth actuatable switch is open so that the resistive load isnot coupled to the regulated bus.

In another embodiment, where during a second state power from the PVinverter is supplied to the external electrical panel and to theregulated bus, the plurality of actuatable switches are configured suchthat: the first actuatable switch couples the PV inverter to theexternal electrical panel; the second actuatable switch couples theregulated bus to the PV inverter; a third actuatable switch couples theregulated bus to the battery and charge controller to charge a battery;the fourth actuatable switch couples the VFD inverter to the regulatedbus; and the sixth actuatable switch is open so that the resistive loadis not coupled to the regulated bus.

In another embodiment, where during a third state the VFD inverterprovides an in-specification grid voltage waveform to the PV inverter,the plurality of actuatable switches are configured such that: the firstactuatable switch couples the PV inverter to the regulated bus; thesecond actuatable switch is open so that the regulated bus is notcoupled to the external electrical panel; the fourth actuatable switchcouples the VFD inverter to the regulated bus; and the sixth actuatableswitch is open so that the resistive load is not coupled to theregulated bus. A battery coupled to the battery and charge controllermay be configured to power the VFD inverter, and the VFD inverter may beconfigured to provide the in-specification grid voltage waveform to thePV inverter.

In another embodiment, where during a fourth state power from the PVinverter is supplied to the generator to charge up mechanical energy ofthe rotatable flywheel, the plurality of actuatable switches areconfigured such that: the first actuatable switch couples the PVinverter to the regulated bus; the second actuatable switch is open sothat the regulated bus is not coupled to the external electrical panel;the third actuatable switch couples the regulated bus to the battery andcharge controller, and the battery and charge controller power the VFDinverter; the fourth actuatable switch couples the VFD inverter to aprimary winding of the generator; the fifth actuatable switch is open sothat the generator is not coupled to the external electrical panel; andthe sixth actuatable switch is controlled to maintain the regulated buswithin a grid voltage specification waveform by providing residual powerfrom the PV inverter to the resistive load. The VFD inverter may beconfigured to provide a variable frequency and voltage waveform to thegenerator to charge up the mechanical energy of the rotatable flywheel.During a fifth state the fourth actuatable switch may couples the VFDinverter to a secondary or auxiliary winding of the generator.

In another embodiment, the plurality of actuatable switches also includea seventh actuatable switch configured to selectively couple theregulated bus to a substantial short circuit.

In another embodiment, where during a sixth state power from thegenerator and rotatable flywheel is supplied to the external electricalpanel, the plurality of actuatable switches are configured such that:the first actuatable switch couples the PV inverter to the regulatedbus; the second actuatable switch, the third actuatable switch, and thesixth actuatable switch are controlled to maintain the regulated buswithin a grid voltage specification waveform; the fourth actuatableswitch is controlled to adjust generator efficiency, power factor, andfrequency; and the fifth actuatable switch is closed to couple thegenerator to the external electrical panel.

In another embodiment, the external electrical panel is coupled to anenergized grid, and a waveform of the VFD inverter phase locks with awaveform of the energized grid.

In another embodiment, the external electrical panel is coupled to abattery/inverter system, and a waveform of the VFD inverter phase lockswith a waveform of the battery/inverter system.

In yet another embodiment, the PV inverter is coupled to abattery/inverter and a battery storage system, and a waveform of the VFDinverter phase locks with a waveform of an islanding inverter.

In accordance with another embodiment, a microgrid system controllerincludes a regulated bus; a battery and charge controller switchablycoupled to the regulated bus; a multiple-phase VFD inverter coupled tothe battery and charge controller; a generator physically coupled to arotatable flywheel and electrically coupled to the multiple-phase VFDinverter; a resistive load switchably coupled to the regulated bus; anda plurality of actuatable switches. An output of the multiple-phase VFDinverter drives at least one of (i) a primary stator winding of thegenerator, or (i) a secondary stator winding of the generator. Theplurality of actuatable switches include a first actuatable switchconfigured to selectively couple a PV inverter to the regulated bus orto an external electrical panel; a second actuatable switch configuredto selectively couple the regulated bus to the external electricalpanel; a third actuatable switch configured to selectively couple theregulated bus to the battery and charge controller; a fourth actuatableswitch configured to selectively couple the generator to the externalelectrical panel; and a fifth actuatable switch configured toselectively couple the resistive load to the regulated bus.

In accordance with another embodiment, a microgrid system controllerincludes a regulated bus; a balancer comprising battery storage, thebalancer coupled to an output of a PV system and coupled to theregulated bus; a battery and charge controller switchably coupled to theregulated bus; a VFD inverter coupled to the battery and chargecontroller and switchably coupled to the regulated bus; a generatorphysically coupled to a rotatable flywheel and a motor electricallycoupled to the VFD inverter, the generator switchably coupled to anexternal electrical panel; a resistive load switchably coupled to theregulated bus; and a plurality of actuatable switches. The plurality ofactuatable switches include a first actuatable switch configured toselectively couple the regulated bus to the VFD inverter; a secondactuatable switch configured to selectively couple the regulated bus tothe battery and charge controller; a third actuatable switch configuredto selectively couple the generator to an external electrical panel; anda fourth actuatable switch configured to selectively couple theresistive load to the regulated bus.

In an embodiment, the balancer comprises direct current (DC) sidebattery storage.

In another embodiment, the VFD inverter is a multi-phase VFD, the motoris a multi-phase motor, and the generator is a single-phase generator.

In yet another embodiment, the microgrid system controller also includesa converter switchably coupled to the regulated bus, wherein theconverter is configured to produce a storable energy source from directcurrent (DC) power; and a motor coupled to the converter and to thegenerator, the motor configured to drive the generator and rotatableflywheel.

In accordance with another embodiment, a microgrid system controllerincludes a regulated bus coupled to an output of a PV system; a batteryand charge controller switchably coupled to the regulated bus; amulti-phase VFD inverter coupled to the battery and charge controllerand switchably coupled to the regulated bus; a multi-phase generatorphysically coupled to a rotatable flywheel and coupled to themulti-phase VFD inverter, the multi-phase generator switchably coupledto an external electrical panel; a resistive load switchably coupled tothe regulated bus; and a plurality of actuatable switches. The pluralityof actuatable switches include a first actuatable switch configured toselectively couple the regulated bus to the three-phase VFD inverter; asecond actuatable switch configured to selectively couple the regulatedbus to the battery and charge controller; a third actuatable switchconfigured to selectively couple the three-phase generator to theexternal electrical panel; and a fourth actuatable switch configured toselectively couple the resistive load to the regulated bus.

In an embodiment, the multi-phase VFD inverter is a three-phase VFDinverter and the multi-phase generator is a three-phase generator.

In accordance with yet another embodiment, a microgrid system controllerincludes a battery storage device coupled an output of a PV system; aregulated bus coupled to the battery storage device coupled; a VFDinverter switchably coupled to the regulated bus; a generator physicallycoupled to a rotatable flywheel and coupled to the VFD inverter, thegenerator switchably coupled to an external electrical panel; aresistive load switchably coupled to the regulated bus; and a pluralityof actuatable switches. The plurality of actuatable switches include afirst actuatable switch configured to selectively couple the regulatedbus to the VFD inverter; a second actuatable switch configured toselectively couple the generator to the external electrical panel; and athird actuatable switch configured to selectively couple the resistiveload to the regulated bus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a schematic diagram of a microgrid system controlleraccording to an embodiment.

FIG. 1B shows a schematic diagram of a microgrid system controllerhaving an integrated load according to an embodiment.

FIG. 1C shows a schematic diagram of a microgrid system controllerhaving a starter switch according to an embodiment.

FIG. 1D shows a schematic diagram of a microgrid system controllerincorporating an electrical-panel-based load switch system according toan embodiment.

FIG. 1E shows motor or generator startup circuitry for reduced batteryusage according to an embodiment.

FIG. 2A shows a front-side view of an exemplary microgrid systemcontroller with a front cover removed according to an embodiment.

FIG. 2B shows a side view of an exemplary microgrid system controlleraccording to an embodiment.

FIG. 2C shows a back-side view of an exemplary microgrid systemcontroller with central and front covers removed according to anembodiment.

FIG. 2D shows a back view with a back cover removed of an exemplarymicrogrid system controller according to an embodiment.

FIG. 2E shows a back view of an exemplary microgrid system controllerwith a flywheel removed according to an embodiment.

FIGS. 2F-2J show alternative views of air inlet and outletconfigurations of exemplary microgrid system controllers according tosome embodiments.

FIG. 3 shows a view of an interior of an exemplary microgrid systemcontroller having a ducted heater according to an embodiment.

FIG. 4A shows a schematic view of an exemplary circuit having a passiveovervoltage power dump according to an embodiment.

FIG. 4B shows a schematic diagram of an exemplary circuit having anagile load dump circuit according to an embodiment.

FIG. 4C shows a schematic diagram of an exemplary circuit having a fastisolator circuit according to an embodiment.

FIG. 5A shows a schematic diagram of a microgrid system controlleraccording to an embodiment.

FIG. 5B-5C show power flow through a microgrid system controller in agrid-connected idle state according to some embodiments.

FIG. 5D shows a schematic diagram of a microgrid system controller in anearly step of a turn-on procedure according to an embodiment.

FIG. 5E shows a schematic diagram of an a microgrid system controllerwith photovoltaic (PV) inverters sourcing power according to anembodiment.

FIG. 5F shows power flow through a microgrid system controller to anappropriately oriented secondary or auxiliary winding according to anembodiment.

FIG. 5G shows power flow through a microgrid system controller in anoperation state according to an embodiment.

FIG. 6A shows a schematic diagram of a grid-connected system that mayfurther comprise a PV inverter and battery/inverter system according toan embodiment.

FIG. 6B shows a schematic diagram of a microgrid buffer comprising anexternal islanding device such as an AC-side battery or inverteraccording to an embodiment.

FIG. 6C shows a schematic diagram of an exemplary DC-fed battery storageaccording to an embodiment.

FIG. 7 shows a schematic diagram of a microgrid system controllercomprising a DC power input and a single-phase AC power output accordingto an embodiment.

FIG. 8 shows a schematic diagram of a microgrid system controllercomprising a DC power input and a three-phase AC power output accordingto an embodiment.

FIG. 9 shows a schematic diagram of a microgrid system controllercomprising alternative DC-side storage according to an embodiment.

DETAILED DESCRIPTION

Distributed energy generation is key to a resilient energy supply, butdistributed resources like solar power do not have any intrinsic surgecapability like that provided by the angular momentum of a generator.Without some form of dispatchable energy storage, power surges, e.g.,those produced when charging capacitors or starting or stopping a largemotor, cause voltage fluctuations that can disrupt or damage otherconnected equipment. Moreover, most solar inverters can only supplypower to a stable, well-regulated grid. As soon as the grid goes down, asolar array and conventional inverter turn off. This radically limitsthe effectiveness of solar power as an emergency or fail-safe powersource.

An “isolated node” as used herein may be a subset of interconnectedpower circuits, sources, and loads that is permanently or temporarilyelectrically isolated from the grid. As used herein, a “micro-grid” isthe collection of circuitry, loads, sources, and control electronics inan isolated node.

As used herein, a switch may comprise anything that substantiallychanges the resistance to conduction across a circuit in response to aparticular actuating stimulus, including a mechanical switch, relay,circuit breaker, thyristor, silicon-controlled rectifier (SCR), triodefor alternating current (TRIAC), solid-state relay,metal-oxide-semiconductor field-effect transistor (MOSFET), insulatedgate bipolar transistor (IGBT), transistor, vacuum tube, etc. An“actuating stimulus” as used herein may be anything that prompts aconductive state change in a switch, e.g., motion, force, torsion,acceleration, gravity, magnetism, electrostatic force, temperature,voltage, current, etc.

As used herein, an “actuatable switch” may be a switch whose state canbe controlled by a signal, such as a relay, transistor, motorizedmechanical switch, etc.

As used herein, a “generator” may be an electrical machine that convertsmechanical work to electricity. A “motor” may be an electrical machinethat converts electricity to mechanical work. Some embodiments describedherein may use an electrical machine that functions both as a motor andgenerator, herein called a motor/generator.

Alternating current (AC) may be an oscillating current or voltage(consistent with common usage) having a substantially zero mean valueand usually a sharply peaked primary frequency herein called the ACfrequency.

Line frequency may be the local standard AC frequency.

Direct current (DC) may be a current or voltage (consistent with commonusage) having a substantially constant value or non-zero spectralcomponent much lower than line frequency.

As used herein, a vanelet may be a streamlined protuberance thatpassively influences local air flow.

As used herein, a “dynamic line measurement” may comprise aninstantaneous or phase-averaged measurement of one or more of linecurrent, voltage, phase, frequency, power factor, waveform defect, ordeviations from sinusoidality.

As used herein “coordinates” may refer to an action of a controller thatinvolves transmitting and receiving a purposeful signal that maycomprise one or more of: setting or reading a digital handshaking line,setting or reading an analog voltage, setting or reading an analogcurrent, setting or reading a waveform frequency or phase, transmittingor receiving digital data, applying a pulse-width-modulated signal,actuating a relay or switch, powering the input or reading the output ofan optocoupler, driving the input or reading the output of a logic gate,driving at transistor gate driver, driving a transistor terminal, etc.

As used herein “measures” may refer to an action of a controller thatprovides the controller with information about a parameter. This actionmay comprise one or more of: reading an analog signal, analog-to-digitalconversion, analog communication, digital communication, deduction,inference, calculation, etc.

FIG. 1A is an overview diagram of a microgrid system controller 1000according to an embodiment. In this embodiment, a household microgrid iscreated using a photovoltaic array 1002 and string inverter 1004.Alternatively, an array of microinverters may be used. These invertersmay be non-islanding. In this embodiment, the power grid 1005 connectsto a power entry panel 1006.

In some embodiments the inverter output directly connects to thesubpanel via 1007. In other embodiments it connects to 1102 through 1008via actuatable switch 1508.

Element 1010 is a service disconnect switch/breaker and elements 1012are individual circuit breakers. In microgrid operation, switch 1010 orits equivalent is open, isolating the wiring in the house from the grid.The width of the schematic power connections may indicate the order ofmagnitude of power, e.g., a doubling of the line width corresponding toa 10× increase in peak power flow, but this depiction is not intended tobe limiting. Power connections indicated by dashed lines are alternativeconnections. Connections 1020 and 1030 may be breakable connection topower outlets. Connections 1022 and 1032 may be wired connections, made,for example, by an electrician.

The controller system 1000 comprises an “inertial power module” 1100with primary power circuit 1102 comprising a motor/generator 1200, aflywheel assembly 1300, and an aerodynamic cowling assembly 1400.

Some motor/generators 1200 comprise one or more of: rotor electronics1210, stator control electronics 1220, rotor to stator communicationschannel 1230, main rotor winding 1250, auxiliary rotor winding 1252,stator winding 1260, and auxiliary stator winding 1262.

Some flywheel assemblies 1300 comprise a flywheel disc 1302, a flywheelhub 1304, and a flywheel retainer 1306.

Some aerodynamic cowling assemblies 1400 comprise an inlet 1410 andoutlet 1412. Airflow induced by flywheel motion 1414 may be usedgainfully in some embodiments, e.g., for drying, applying force-airconvection, ventilation, attic ventilation (e.g., mounted near 1090).Some embodiments comprise outlet 1412 features that modify volumetricflow via air entrainment e.g., a diffuser, nozzle, ejector.

Some cowling designs according to an embodiment produce a circulatoryairflow 1420 that passes over the motor/generator windings for enhancedcooling.

Some cowling designs comprise at least one vanelet 1430 to redirectflow, suppress or enhance a secondary flow, etc.

The system further comprises a “source-control module” 1500. In someembodiments this module comprises a user portable housing 1502 havingbreakable connections 1504 that provide for relocating and re-purposingthe module when the microgrid is not active. Element 1506 is anactuatable switch controlled by signal 1507 that connects anddisconnects the generator output from the microgrid. In some embodimentselement 1508 is an actuatable switch controlled by 1509 that connectsand disconnects the inverter output from the generator output. In someembodiments at least one of: switch 1506 or switch 1508 are proximal toservice disconnect 1010 such that their mutual on-states may bemechanically or electrically inhibited.

A controller 1510 measures at least one dynamic line measurement (1512)of the microgrid and at least one dynamic line measurement (1514) of amotor/generator stator circuit 1532. Controller 1510 further coordinates(1516) a battery charge controller and battery bank module 1520. The DCbus of the battery 1524 is used by a bridge-circuit 1530. In someembodiments 1530 is an inverter. In some embodiments, this inverter canfunction as a phase of a variable frequency AC, DC, or brushless DCmotor drive having output 1532. In some embodiments this inverter canfurther function as an islanding voltage-source AC line inverter,supplying a power outlet 1560.

Some embodiments further comprise second bridge circuit 1540. In someembodiments 1540 is an inverter whose output 1542 can drive a winding ofa motor. In some embodiments 1540 can further function as an islandingvoltage-source AC line inverter supplying outlet 1562. Some embodimentsalternatively comprise a switchable phase-shifting circuit 1550 toproduce signal 1542 in lieu of 1540.

Some source-control modules further comprise a subsystem 1580 that mayprovide functionality that is helpful during an outage or emergency.Element 1582 comprises one or more low-voltage DC chargers, such as USB,USB-C, etc.

Element 1580 may comprise a connection to an automotive starting batteryor other such battery. In some embodiments, this allows a deadautomotive battery to charge from power supplied by the battery moduleor microgrid. In some embodiments, this allows the battery module tocharge from the external battery, e.g., in the event the battery moduleis too depleted to spin up the flywheel.

Element 1580 may comprise one or more lights 1586, e.g., an LED, a UVsterilization light, a strobe, a beacon and a radio receiver ortransceiver 1588.

Some embodiments comprise a “load-control module” 1600. In someembodiments, this module may have a housing 1602 that allows the moduleto be portable. In some embodiments the module is connected breakably toan electrical outlet on the microgrid 1030. This module comprises acontroller 1610 that measures at least one line parameter 1612, e.g.,voltage or frequency, and controls at least one actuatable switch, e.g.,1620, 1630 to a line load. Some embodiments comprise load 1624comprising a forced-convection heating element. In some embodiments,this load may be used as a space heater or dryer or may be used as anenergy dump to the outside environment by appropriately locating theportable load-control module. In some embodiments, a user may plug analternate load into an output of the load-control module, e.g., 1634.Some load controllers comprise a plurality of controlled switches andoutlets 1634.

Some source-control modules may comprise at least one switch to oneload.

Some load-control modules operate based on line frequency and voltagespecifications, applying at least one load when the frequency, rmsvoltage, or instantaneous voltage is out of specification. Some loadcontrol modules switch at least one load on and off fast enough toperform real-time voltage-defect and transient suppression.

Some such load-control modules may operate autonomously from the rest ofthe microgrid system. Some alternative embodiments comprise acommunication channel 1640 to the power source controller. Somealternative embodiments comprise a communication channel 1650 to aremote load-control system 1700 located substantially at a breaker panelor subpanel.

Element 1700 is a breaker panel load control system. Some embodiments ofthis system comprise a master-switch indicator 1702 which senses theposition of the service disconnect and can report this status remotely.Some master-switch indicators 1702 further comprise an actuator,allowing controller 1700 to disconnect from the grid automatically. Someembodiments further comprise a grid-side signal sensor to determine whengrid power has returned. Some embodiments report any phase or frequencyerrors between the microgrid and the grid over communications channel1650 to the load controller or 1720 to the power source controller, sothat controllers can take actions, e.g., shed loads, add loads, changethe power factor, actively spin up or spin down the flywheel, etc. soerrors can be substantially nulled, allowing a synchronous reconnect tothe grid. In addition, a communication channel 1720 to the loadcontroller may be used as a safety interlock to prevent power from themicrogrid from being exported to the grid during an outage or to prevent1506 from being closed while the microgrid and grid are asynchronous. Insome embodiments, 1702 is a position-indicating interlock switch andcommunications channel 1720 is a wired connection to the power-sourcecontroller.

In some embodiments, a startup of the system can be initiated by a useror automatically, e.g., via a real-time clock, photosensor, wirelesscommand, etc.

In some embodiments at startup, the operation of bridges and phase-shiftfunctions are coordinated via signals 1518 to initiate motion of or“start” the motor/flywheel. In some embodiments it may be desirable toprevent microgrid loads from experiencing the voltage waveforms producedduring the starting of the motor/generator because the voltages andfrequencies are out of grid specification and the motor-drivers, e.g.,1530, 1540, 1550, or battery module 1520 may not have the capacity todrive microgrid loads. Therefore, in some embodiments this initiation ofthe motor may occur with switch 1506 open until the generator issubstantially at its speed setting.

In some embodiments, switch 1508 is open during motor/generator startup. In other embodiments, during startup, the switch 1508 is closedbetween the waveform 1102 and the inverter because grid-tied invertersmay not require isolation during the ramp up of the generator, however,the inverter may need to be isolated from all panel loads.

In some embodiments, when the motor/generator has reached a sufficientrotation rate, e.g., 10% to 90% of the line-synchronous rotation rate,the phase-shift circuit 1550 or auxiliary winding driver 1540 may beswitched off.

In some embodiments, when the motor/generator has reached linefrequency, the controller 1510 maintains a tight frequency and voltagecontrol of its bridge 1530 to maintain frequency. If not alreadyconnected, the circuit 1102 is electrically connected to the inverter orinverters, which may sense a valid grid signal and begin their ownstartup delay timers, which may typically elapse after two to fiveminutes after which the inverters begin to deliver power synchronouslyto circuit 1102. At this point, there may be an excess of energy flowingto the generator, which may raise the rotation frequency, voltage, orchange the direction or magnitude of a flowing current. The controller1510 may sense this state and change to a new starting mode. In someembodiments the controller may operate bridge 1540 such that a reversecurrent flows to recharge batteries module 1520. The controller 1510 mayclose a connection, e.g., switch 1506 to allow power to flow through themicrogrid. The controller may communicate to an external device.

In some embodiments, when the housing 1502 is removed from its breakableconnections 1504, the operating mode can convert to battery-powered ACinverter. In some embodiments, the removal of the module physicallyexposes at least one power outlet for use, e.g., 1560, 1562.

FIG. 1B shows an alternative embodiment of a microgrid system controlleraccording to an embodiment. In this embodiment, the controller 1000 iswired through a switch to the inverter. The inverter and microgridsystem controller are connected to breakers 1014 and 1016, respectively.This embodiment further comprises a switch 1570 controlled by controller1510 via signal 1572 that can energize a resistive load 1574. In someembodiments this resistive load is physically disposed proximal to aflow outlet 1412 such that induced air flow 1414 passes over the heatingload such that heat is convected from the load. Some such embodimentsmay obviate a separate load controller 1600. Some embodiments comprisesensing of a line parameter from the inverter 1578. Some embodimentscomprise sensing of a line parameter from the motor/generator 1579. Someembodiments may comprise one or more power sockets 1576.

FIG. 1C shows an alternative embodiment comprising a “starter switch”1580 and single breaker connection 1016. When the microgrid is idle oroperating, the switch 1580 may quiescently connect the inverter outputto line 1022 to the breaker. For some time period when the microgrid isstarting, signal 1582 from controller 1506 switches the inverterconnection to 1008, feeding the line signal produced by the generator tothe inverter. When power is detected flowing from the inverter, theswitch 1506 may be closed and the switch 1580 may optionally be returnedto its quiescent state.

In some embodiments, when power flows from the PV inverter, a powercontroller, e.g., 1510 measures the available power. In someembodiments, the measurement is obtained in part by communication withthe inverter. In some embodiments, the power controller monitors atleast one line parameter measurement. In some embodiments, the powercontroller determines the duty-cycle of a resistive load, e.g., 1574that maintains a substantially steady motor speed, AC voltage, ACfrequency, etc. In some embodiments, the controller reports thisavailable power to a second device. In some embodiments knowledge of theinstantaneous available power is used to manage loads.

FIG. 1D shows a schematic diagram of a microgrid system controllerembodiment that employs a breaker-panel-based automated switch controlsystem 1700. Power to and from the microgrid system controller isconnected to breaker actuated at 1708 via conductors 1590. In somealternative embodiments, the switching is performed manually. In thisembodiment, the inverter is connected to a breaker at actuation station1706. The microgrid system controller is connected to a breaker atactuation station 1708. Actuator stations 1710 and 1712 connect to aplurality of loads that may have different priorities.

In this embodiment, when the grid goes out, actuation station 1702disconnects the panel from grid service. Actuation stations 1710, 1712,etc. turn off all loads. In some embodiments, one or both of stations1706 and 1708 are switched off. When the microgrid system controller isup to its specified speed, stations 1706 and 1708 are closed, sendingthe microgrid signal to the inverter. When there is excess poweravailable from the inverter, the actuation controller may switch onloads, in some embodiments according to a priority that may be timedependent.

Microgrid Interlocking

To prevent the possibility of exporting power to the grid during anoutage (non-islanding), an interlock on a service disconnect switch maybe used. In some embodiments this interlock comprises aposition-indicator 1702. In some embodiments this interlock comprises alockout lever or mechanism that prevents reconnection to the grid whilethe interlock is satisfied. In some embodiments the interlock is inmechanical or electrical communication with a switch 1806, 1506, or1508, in such a way to prevent the simultaneous closure of the serviceswitch 1010 and system power switch. Some embodiments provide a softwareor firmware mediated control over interlocking, since a rigid interlockmay prevent the system from operating beneficially in normalnon-islanded circumstances. In some such embodiments, the sourcecontroller 1510 may monitor the microgrid waveform like a standard PVinverter does and switch off if the grid has exceeded its specifiedlimits for longer than the specified duration. In some embodiments, thismay involve the microgrid system controller periodically switching offand observing the waveform. In some embodiments, this may involve themicrogrid system controller periodically applying a load that issubstantial enough that it would require valid grid power to maintainand then monitoring the effect of the load. In some embodiments, themicrogrid system controller switches off its output when it senses achange in the grid state. In some embodiments, the microgrid systemcontroller switches operation when it detects that the grid has gonedown by performing one or more of: actuating a service disconnect switchopen, e.g., via 1702 or its equivalent, initiating load shedding. Insome embodiments, a non-islanded microgrid system controller acts toisolate from the grid while the local line parameters are within theinverter specifications, so the inverters do not trip or stop producingpower during the conversion to islanding.

In some embodiments, the microgrid system controller may perform anautomatic grid-reconnection procedure comprising sensing a valid gridsignal for a specified interval, synchronizing its flywheel motion tothe valid grid signal, then re-closing the service disconnect 1010,e.g., via 1702. In some embodiments, a controller in the microgridsystem 1000 may automatically initiate load adding as full service isrestored.

Microgrid Startup Procedure

These components work in concert to create a microgrid by a micro-gridstartup sequence of steps in which the node is isolated, a grid-signalgenerated in the microgrid and components are switched in and out tomaintain the microgrid. One embodiment of a micro-grid startingprocedure comprises one or more of the steps:

-   isolating or ensuring isolation from the grid (switch 1010 to off    position),-   opening a switch 1012 to a load circuit,-   opening all breakers to load circuits,-   opening a switch 1506,-   spinning-up the generator 1200 connected to the flywheel 1300 to    stabilize the voltage waveform and frequency within a specified    range,-   closing a source switch 1508 to one or more renewable resource,    e.g., string inverter 1004 or microinverter, and-   waiting an interval until source power is detected.

If source power is detected in the interval, the system may switch to aMicrogrid Regulation Mode.

If no source power is detected during the interval, the system mayswitch to a Microgrid Shutdown Procedure.

Alternative Microgrid Startup Procedure

Some embodiments follow an alternative startup procedure wherein a smallvoltage-source sine-wave inverter circuit feeds a valid grid signal tothe PV inverter with substantially no other battery load. If the PVinverter fails to begin supplying power during a startup interval, thecontroller turns the inverter circuit off, establishing a low-power idlestate until the startup mode is reactivated manually or automaticallyafter an interval.

If the PV inverter begins to supply power, the controller maintains avalid grid signal via high-speed regulation of its resistive load, whileit soft-starts rotation of the generator and flywheel and brings theflywheel into synchronization with the PV inverter. Then the controllercloses a switch between the generator and PV inverter to create themicrogrid. The system may then switch to the Microgrid Regulation Mode.

FIG. 1E shows such an alternative embodiment of theinverter/motor/generator startup circuitry 1800, comprising a selectorswitch or its equivalent 1802. In the startup state position (shown),switch 1802 connects the bridge 1530, operated as a sign-wavevoltage-source inverter, to conductors that are in electricalcommunication directly or through a network of switches and conductorsto at least one PV inverter 1004. At startup, this supplies a valid gridwaveform to the inverter for the duration of the PV inverter startupdelay interval. When the inverter begins to apply power, apulse-width-modulated (PWM'd), constant-on-time modulated or otherwisemodulated, and, in some embodiments, low-pass filtered switch (e.g.,1570) to the a substantially resistive load (e.g., 1574) regulates theAC waveform supplied by the inverter while the excitation from 1530 isremoved, in some embodiments, gradually. Switch 1802 is then thrown bysignal 1804, connecting the bridge 1530 to one or more stator windingsof the motor generator. The bridge, in concert with zero or more of: asecond bridge, a phase-shift circuit 1550, or a power-factor controlcircuit, soft-starts the motor generator, e.g., via a variablevoltage-frequency control scheme. In this position of switch 1802(opposite that shown) at least one line parameter of the generatorwaveform may be sensed (e.g., via 1514) by the controller and comparedto that sensed (e.g., via 1578) from the PV inverter. The controller maythen apply a control algorithm on one or more of the PWM'd resistiveload, the motor-driving waveform to lock, or substantially match thevoltage and frequency of both sinusoids. When these waveforms, presentacross switch 1806, are sufficiently similar, the controller may close1806 via control signal 1808, electrically connecting themotor/generator to the PV inverter to create a microgrid that istolerant of surges and power spikes.

The alternative arrangement of 1800 may confer the advantage that thebattery usage during the PV inverter startup delay is dramaticallyreduced, since there may be no charging of the flywheel and motorlosses. It may confer the advantage that the battery usage during themotor/generator startup is dramatically reduced, since AC power isavailable to the battery charger circuitry. In some embodiments,substantially all of the power to spin up the generator is supplied viathe PV inverter output. In some embodiments, the power source to aninverter is switched from battery to the PV inverter or its rectifiedoutput.

In some embodiments switch 1806 is proximate to service disconnect 1010such that they are prevented mechanically or electrically fromsimultaneously being in their on-state.

The arrangement 1800 may have the further advantage that it can be usedto synchronize the flywheel to an established grid or secondarymicrogrid, allowing the system 1000 to be used for normal ornon-islanded grid or microgrid enhancement, such as surge limiting,transient suppression, power factor correction, etc. In some suchembodiments, forced air from the subsystem 1100 may be used to avail,such as for attic ventilation, drying, forced convection past a radiatoror heat-transfer unit, air circulation, etc., providing value to offsetthe energy use of the motor.

In such embodiments the controller may allow service switch andgenerator switch 1806 to be simultaneously closed under conditions of avalid grid signal.

Some systems may be installed where islanding is guaranteed, e.g., wherethere is no grid service 1005. In such cases, a grid controller mayoperate with an islanding interlock defeat, a firmware, software, orjumper configuration that eliminates or unconditionally satisfiesislanding checks.

Microgrid Regulation Procedure

The aim of the regulation procedure is to maintain a high-quality,accurately specified grid waveform despite sporadic loads and surges. Insome embodiments, regulation entails the coordination of a plurality ofsources and sinks or loads. Excess sourced energy may increase theflywheel rotation rate and generator root mean square (RMS) voltage.

A deficit of sourced energy may decrease the flywheel rotation rate andgenerator RMS voltage, therefore a part of regulation is a process ofmaintaining the RMS voltage, frequency, or both. In some embodiments,this regulation comprises actuating at least one switch (e.g., 1620,1630, 1570) to a load or to control battery charging (1516) to establisha time-averaged balance between energy production and usage. Rather thanload-shedding when a temporarily unsustainable power deficit isencountered, some embodiments supplement power from the PV system by oneor more of: allowing the flywheel rotation to drop or converting batterypower to AC power via 1530. When the unsustainable load relaxes, thecontroller recharges the batteries and the flywheel. In someembodiments, the controller (e.g., 1220 or 1510) charges the flywheelsubstantially near the maximum specified frequency to provide maximalload-surge impulse capacity.

A second part of the regulation may be regulating the instantaneousvoltage waveform to mitigate fast transients. In some embodiments, thisregulation is largely provided by the action of the flywheel/generator.In some embodiments, this regulation further comprises a controlleractuating a fast switch to a load (1610 actuating 1620 to 1624, or 1510actuating 1570 to 1574). Some embodiments may provide a separateproximal local load that is actuated only for fast transients thatavoids noise filtering and line inductance effects of remote loads. Someregulations may comprise a high-frequency pulse-width signal modulatedby an instantaneous error voltage. Some embodiments or control loopscomprise an error signal term that may be high-pass filtered to excludeline frequency and frequencies that the generator can mitigate.

Some regulations control loops dynamically adjust a parameter of thetarget voltage, e.g., amplitude, frequency, instantaneous phase, etc.,to maintain synchronization with the flywheel/generator motion. Someembodiments gradually increase or decrease one or more of: voltageamplitude target or voltage frequency target to re-charge the flywheelor prevent excessive flywheel frequency, respectively.

A third part of regulation may be establishing a desired power factor,e.g., substantially unity. In some embodiments this regulation comprisesa control circuit directly (e.g., 1230) or indirectly (e.g., 1220, or1510) regulating a quasi-DC field current in a rotor winding.

A fourth part of regulation may be automatically load shedding or loadadding, e.g., via a load controller 1610 and at least one switch (e.g.,1630) to a user-selectable load, e.g., a water heater on outlet 1634.Some embodiments comprise a load actuation system (e.g., 1700) that canactuate circuit switches at a power panel. Some embodiments comprise ahome-automation system. In some embodiments a load controller (e.g.,1610, 1700) is coordinated with a second controller, e.g., the sourcecontroller 1510. In some embodiments a load controller (1610) takesindependent action based on a measured (1612) line parameter. Some loadcontrollers 1610 may coordinate a load actuation system 1700.

Microgrid Shutdown Mode

It may be desirable to effect a gradual shut-down of the microgid, e.g.,if the power source has dropped below sustainable levels orminimal-load. In such instances, some systems will have performedload-shedding as the available power levels drop. Some embodimentsprovide regenerative charging of the on-board batteries from the storedflywheel energy. Some embodiments may attempt to restart the microgridperiodically, in some cases, if an internal model or clock indicatespower should be available. For example, the microgrid may power downtemporarily because of passage of a dark cloud or temporary casting of ashadow and it may be desirable to restore power automatically after thisevent passes.

Synchronous Condenser

A key source/sink in some embodiments is a synchronously rotatinggenerator 1200 having intrinsic or attached rotational inertia 1300,known as a “synchronous condenser,” that is sufficient to supply or sinkrated power spikes. In some embodiments, the stored flywheel energy issufficient for the generator to supply an impulse long enough to satisfythe surge load without while maintaining a voltage waveform withinspecifications, including frequency. Some embodiments comprise agenerator that comprises novel design elements to maximize the stiffnessof its current source/sink versus phase angle between the rotor fieldangle and synchronous stator field. In some embodiments, the flywheelgenerator has a storage capacity at rated power between 0.05 s and 10 sand preferably between 0.3 s and 3 s before the AC frequency drops belowa specified minimum.

Distributed Energy Resource

Some embodiments may comprise a distributed energy resource, such as aninverter 1004 and photovoltaic (PV) array 1002 or an equivalent array ofmicro-inverters and PV panels. The illustration of the microgrid systemin relation to a single PV array is not intended to be limiting. Someembodiments may control a microgrid fed by one or more energy resourcesderived from one or more of: solar, wind, water motion, chemical energy,flywheel motion, gravitational potential energy, elastic energy,compressed fluid, phase-change energy, etc.

Legacy PV inverters may typically operate to produce substantiallymaximal electrical power available from the solar panels. Some invertershave operating modes where their power setting can be limited oradjusted in a variety of ways, e.g., voltage-frequency adjustments, etc.Some inverters adjust their output according to the RMS grid voltage.Such enhanced inverter operations may help to achieve a low-frequencybalance between production and consumption. Some inverters adjust theiroutput according to the instantaneous grid voltage, allowing ahigher-frequency source-regulation capability.

Some embodiments are designed to work without coordination or signalingwith the inverter apart from the microgrid voltage waveform. Anadvantage of this minimal coordination may be a reduction in engineeringeffort to adapt to third-party inverters and an increase in the numberof installations that can be serviced by the apparatus.

Some embodiments are designed to work with an inverter whose voltage andfrequency specifications can be adjusted from tight grid-connectedranges to more permissive ranges or whose grid-voltage checking may besoftware or hardware disabled. Such systems may have the advantage ofrequiring less flywheel energy storage, e.g., smaller physical size,mass, or rotation rate.

Auxiliary Load

Some embodiments comprise one or more auxiliary loads (e.g., 1624, 1634,1574) that can be switched on and off to achieve a time-averaged balancebetween production and consumption. Some loads convert surpluselectricity to one or more of heat, light, electrochemical reactions,battery energy, electric vehicle charge, gravitational potential energyof a mass or fluid, compression or tension of an elastic solid or gas,pressure in a fluid or solid, phase change of a gas, fluid, or solid, amanufacturing process, evaporation, increased or decreased humidity,etc. Some light outputs may comprise plant, algae, or tissuegrowth-enhancing, heat, or sterilization lights. Some electrochemicalproducts may comprise a storable fuel or oxidizer, e.g., carbon, oxygen,hydrogen, methane, ethane, propane, n-ane, paraffin oil, wax, and thelike. Some pressure products may be used to drive reverse osmosis. Someheat products may be used for hot water, ambient environment control,process, drying, or cooking heat. Some such heaters may be portablydisposed so an end user may position the heat for best effect, e.g.,outdoors if the indoor temperature is too high or in a room where spaceheat is advantageous.

Some auxiliary loads, such as a heating element, can be turned on andoff rapidly (1 μs to 100 s) affording rapid regulation response. Otherloads, such as an air or freon compressor may need to be switched on andoff for longer intervals (e.g., 10 s to 1000 s) to be effective. Someloads, such as lights and heaters, can be driven at intermediatevoltages that may comprise a low-pass filtered PWM'd waveform.

Connection to Auxiliary Loads

In some embodiments, at least one auxiliary load is breakably connectedto the system, e.g., through a conventional power socket and plugarrangement (e.g., 1634). In some embodiments, an auxiliary load orcontroller (1600) may be connected through an extension cord (1040) tothe system or site power 1030 so it can be positioned for best effect,e.g., placing a space heater in a room or outdoors. In some embodiments,an extension cord is retractably connected to the system. Some suchembodiments employ a spiral torsion spring retraction mechanism.

In some embodiments, at least one auxiliary load is connected to themicro-grid via a switch, e.g., a circuit breaker (1012). In someembodiments, the circuit breaker or switch is installed in an electricalpanel (1006) and in electrical communication with site wiring. In someembodiments, site wiring conducts current between the system and anauxiliary load. In some embodiments the system applies an actuatingstimulus to a switch directly (1632) or through an intermediaryactuator, e.g., 1700 via communication channel 1650. Some intermediaryactuators are controlled wirelessly.

Auxiliary Load Controller

In some embodiments, a microcontroller or computer coordinates switchingof one or more auxiliary loads (e.g., 1610 controlling power to 1624 or1634, 1510 controlling power to 1574). In some embodiments, at least oneauxiliary load is pulse-width modulated. In some embodiments, at leaston auxiliary load is “on/off” controlled, herein defined as turned onand off substantially as in normal use.

Regulating the Voltage Waveform and Frequency

The regulation of the voltage waveform and frequency may comprise one ormore of: turning on and off or adjusting the power setting of at leastone auxiliary load, e.g., a heater, an air heater, a water heater, aground heater, an electrolysis unit, an electrochemical process, abattery charger, a light, a growth light, a pump, a well pump, a poolpump, a sump pump, a pool heater, a gas compressor, a gas compressorwith phase change, an air-conditioner, a de-humidifier, an ice maker, adigging mechanism, etc.

Inertial System

Some embodiments of 1100 comprise additional angular inertia over thatof the generator 1200 and further comprise a flywheel system 1300 thatcomprises a flywheel disk (1302), hub (1304), and retainer (1306).

Some flywheel discs 1302 comprise one or more of factory-installedhardware, user-installed fixed-mass hardware, and user-installedvariable-mass hardware. Some variable-mass hardware comprises a flywheelenclosure that has a massive component added to it by a user, such aswater, dirt, gravel, sand, concrete, molten metal, molten lead, moltentin, etc. Some such massive elements may be ubiquity, low-cost, highdensity, low-hazard. Some fixed-mass hardware comprises one or moreround steel discs. Some flywheels comprise a hub apparatus to which oneor more flywheel discs can be attached. In some embodiments, the storagecapacity of the flywheel can be changed by the factory or end user byattaching more or fewer discs, in the manner of a bar-bell. Someflywheel discs comprise more than one kind of metal, e.g., iron or steeland lead or some other inexpensive dense material. Such embodiments mayhave the advantage of reducing the total shipping weight of the systemfor a given rotational energy storage level.

Some disks are produced by stamping, laser cutting, water-jet cutting,and saw cutting, casting, die casting, sand casting, etc. Some flywheelscomprise a plurality of parallel-stacked discs. Some flywheels compriselaminated disks in some embodiments, lamination is achieved by welding,brazing, soldering, epoxying, riveting, mechanical fasteners, etc. Insome embodiments laminated flywheels may include at least one interiordisc containing at least one internal opening to produce an internalcavity in the flywheel. In some embodiments an arrangement of aplurality of openings in internal laminae are disposed away from thedisc rim, to reduce the flywheel mass proportionately greater than therotational inertia, without increasing the exterior wetted area orproducing turbulence. In some alternative embodiments, a plurality ofcast discs having a concavity on one side and a substantially flatopposing side are laminated or connected so the substantially flat sidefaces outward, into the immersion fluid.

Some flywheels further comprise one or more fiducial marks. Somefiducial marks comprise one or more sets of optically distinct marksarrayed circumferentially at one or more radii to facilitate a rotaryencoder function. Some arrays have at least one signaturecircumferential or radial variation or modulation that can be used todetect absolute angle. Some stator-frame-of-reference controllerscomprise an optical element to read or scan the fiducial marks as theyrotate past a sensor to detect flywheel position angle accurately.

Some embodiments comprise a flywheel hub 1302 that transitions betweenthe generator shaft and one or more flywheel disks. Some flywheel hubsaccept a center-tapped or center-drilled tapered shaft. Some flywheelhubs comprise a surface of a mechanical clutch meant to preventdangerous operation or damage in the event of a fault, such as a shortcircuit. In some embodiments, the mating clutch surfaces comprise matingcontacts having one or more of taper, face, or cylinder surfaces. Someembodiments have a mating taper, further comprising a rod that applies acompression between clutch surfaces, and the rod may comprise one ormore of a threaded end, a head, a head with provision for seizing wire,a castle nut, or an elastic element. In some embodiments, thecompressive force applied to the faces is set to produce non-gallingsliding slippage at a set point near the maximum torque setting of thegenerator at maximum peak power. In some embodiments, this applied forceis maintained by elastic deformation of a spring or material. In someembodiments, this elastic element is a Belleville disc spring.

Some hubs further comprise a substantially cylindrical shaft for arotary bearing mounted substantially to motor-generator housing orsupports to ensure that the motor/generator shaft remains sufficientlyparallel with the stator so that the stator and rotor do not come intocontact.

Some embodiments further comprise a flange, the flange furthercomprising at least one feature to prevent relative motion between aflywheel disk and hub. Some such features comprise one or more of ahole, a tapped hole, a pin, an embossment, an indentation, a protrusion,or a keyway. Some flanges comprise one face of a clutch, and some retaina separate elastic element that comprises one surface of a clutch. Insome embodiments the face of a flywheel disc comprises the secondsurface of a clutch. In some embodiments the clutch comprises at leastone indentation and protrusion having a ramp-like interface such that asufficient torque can clear the protrusion from the indentation despitean elastic preload.

Some flywheel hubs further comprise a substantially cylindrical shaftwhich accepts the central opening of one or more flywheel discs. In someembodiments, the shaft has a circular cross section. In otherembodiments the shaft has a shape that interlocks with a feature such asa spline, tooth, or keyway in the central opening of a flywheel disksuch that the disk orientation with respect to the shaft is indexed ormaintained. Some shafts and flywheel openings are toleranced to limitthe maximum run-out of the flywheel.

Some flywheel hubs are configured to accommodate a retainer mechanism1306 to ensure flywheels cannot accidentally or unintentionally escapethe flywheel hub. Some such accommodations comprise at least onecircumferential feature to hold an external retaining ring. Someembodiments comprise a plurality of retaining ring grooves to facilitateflywheels of different thicknesses or disc counts. Some hubs provide amount for an alternative flywheel backing mounting ring 1306. Some hubsallow the installation or removal of one or more flywheel disks withoutdisassembly of anything in the motor/generator/flywheel apparatus otherthan a backing mount or retaining ring.

Some hubs further comprise at least one mass-distribution adjustment toprovide for manually or automatically balancing the flywheel.

Flywheel Balancing

Some embodiments include tolerance shafts, hubs, and flywheel disks toensure to obviate additional balancing operations.

Some embodiments provide for a flywheel validation commissioningprocedure based on one or more of maximum permissible vibrationamplitude, maximum flywheel slip, minimum flywheel inertia, or maximumflywheel inertia. Some embodiments perform validation commission testingat flywheel spin up. Some embodiments perform commission testingcontinuously. Some embodiments perform balance calculationsautomatically from vibration displacement, acceleration, or forcemeasurements. In some embodiments these measurements and calculationsare performed during flywheel spin-up, which may be aborted by thecontroller (e.g., 1510) if excessive or unexpected vibration orsubstantially different-than-expected rotational inertia or resistanceis sensed. Some systems further comprise software that can identifywhere and how much to add, remove or shift mass to balance the system.Some embodiments may automatically make balancing adjustments.

Aerodynamic Design

Lost rotational energy from a disc flywheel operated in an immersionfluid such as air may mostly appear as impelled air motion. Themagnitude of lost energy depends on the details of the housing andcowling around the flywheel, but is of the order of 100 W at 3600 RPMfor a 0.7 m flywheel. This amount of air motion may be useful forcooling the apparatus without requiring additional cooling fins or fans.Some embodiments provide fly-wheel impelled forced air as a desirableside-effect, secondary intent, or primary intent. For example, theflywheel may be configured as an attic ventilation fan, offsetting theidle losses of the flywheel/generator system. Some such embodimentscomprise a generator/flywheel/housing assembly that is disposed in anattic or other area where daytime forced air is useful. Someembodiments, further comprise a motor-controller, battery, and loadcontroller system 1500, 1600 located remotely from thegenerator/flywheel/housing assembly. In some embodiments one or morecomponents of the system can be disconnected from the rest of the systemand operated remotely. In some embodiments, remote operation isfacilitated by one or more of power, signaling, and communications viaexisting building wiring. Some flywheel designs may comprise at leastone vanelet (1430) to enhance or inhibit aerodynamic pumping effect,e.g., having a slight spiral angle directing air radially outward orinward, respectively.

Cowling

Aerodynamic losses and sound production from the flywheel may beparasitic and unwanted. Some flywheels reduce the fluid pressure orviscosity surrounding the flywheel to reduce losses. Some embodimentscomprise a cowling and check valve disposed about the flywheelsubstantially to maintain a vacuum. Some cowlings further surround thegenerator to obviate a vacuum seal around a rotating shaft. Some suchembodiments comprise one or more of a thermal mass, heat pipe, liquidcooling channel, etc. to maintain a safe operating temperature for thegenerator.

Some systems comprise an aerodynamic cowling 1400 designed to minimizenoise and turbulent losses of the flywheel and, in some embodiments,provide a generator operating in atmospheric air. Some such cowlingscomprise at least one internal feature or vane-let 1430 that acts tomaintain an orderly circulation pattern within the cowling. Some suchvane-lets comprise a ridge on a surface. Some vanelets are substantiallycircumferentially disposed. Some vanelets have a radial spiralcomponent. In some embodiments, this radial spiral component angledirects air in opposition with the natural outward angle produced bycentrifugation causing an orderly secondary flow recirculation. In someembodiments, the vanelet angle directs air in concert with the outwardflow angle, producing an orderly radial bulk fluid flow. In someembodiments the cowling further comprises at least one fluid outlet(1412, 1413) for this radial flow. Some cowlings further comprise one ormore aerodynamic ducts (1410, 1412), a plurality of aerodynamicvanelets, openings (1413), slots, holes, tapers, nozzles, etc. tocollect and redirect this radial flow, ideally with low noise and goodpressure recovery. Some external (1430) and internal (1432) cowlingsdirect this flow (1420, through opening 1413) to resupply the bulk flow.In some embodiments this resupply air passes over at least one elementthat requires cooling. In some embodiments a portion of the resupply airpasses through the generator (1420). In some embodiments, resupply airpasses over one or more of: power electronics, heating coils orelements, cooling plates, cooling fins, or heat sinks.

In some embodiments, a portion of the bulk flow (1414) produced by theflywheel is ducted or vented externally (1412), facilitating a use(e.g., ventilation or drying) for what may otherwise be a parasiticload. Some embodiments may duct air to the inlet (1410), e.g., forventilation or air quality maintenance.

Some cowlings comprise a material or composite having acoustic dampingproperties. Some cowlings comprise material having vibration dampingproperties, e.g., having a viscoelastic or mechanical energy absorptiveelement. Some cowlings further comprise a part of the device housing.

Motor/Generator

Some embodiments may comprise a bidirectional power source 1200comprising one or more of an alternator, brushless alternator, brushlessDC motor, brushed alternator, brushed DC motor, induction motor,brushless synchronous motor, or brushed synchronous motor. The motorsmay have salience. Some embodiments may comprise a two-pole motor havinga synchronous rotation rate of 3600 RPM at 60 Hz or 3000 RPM at 50 Hz.

An embodiment of a synchronous motor comprises a two-phase stator and arotor comprising a field winding 1250 and at least one auxiliary winding1252 used to do one or more of: draw power from the stator fields tosupply power to the field winding, damper rotary oscillations, orprovide motor starting torque while operating in an induction mode.

Rotor Electronics

Some embodiments comprise a field control/regulation circuit 1210 in therotor frame of reference. Some controllers comprise a microcontroller incommunication with a second circuit 1220 in the stator frame ofreference. In some embodiments, the communication channel 1230 iswireless, free-space optical, acoustic, electrostatic, magnetic, orelectromagnetic. In some embodiments, electromagnetic transmission isachieved by modulating data at a carrier frequency away from linefrequency (e.g., much higher than line frequency) and coupling thismodulated data into the current or voltage waveform of a rotor windingor stator winding. Electromagnetic reception is achieved by filteringthe modulated data from line-frequency components and demodulation. Insome embodiments, at least one signal is communicated to a rotorcontroller via one or more of: an analog signal, a digital signal, ananalog modulated signal, or a digital modulated signal.

Some rotor controllers 1210 can adjust reactive power production byvarying the field current. Some embodiments can actively trim unwantednon-sinusoidal voltage-output characteristics by superimposing acompensating line-synchronous periodic excitation to the field coil. Insome embodiments, this compensation may allow a generator winding andlamination design to be simpler or easier to assemble, resulting inlower cost. Some controllers contain non-volatile calibration data toachieve this trimming. In some embodiments, a stator-monitoringmicrocontroller (e.g., 1220 or 1510) may communicate voltage-defectfeedback data to the rotor that the rotor controller may use to performself-calibration or adaptive compensation. In some embodiments, adaptivecompensation may allow a generator to correct voltage defects producedby loads or grid non-idealities. In some embodiments, adaptivecompensation may allow a generator to mitigate voltage transients.

At startup, the rotor rotation rate may be zero and there may be anarbitrary angle of the rotor windings with respect to the main statorwindings 1260. This may prevent a rotor from experiencing a startuptorque at some angles. To mitigate this effect some embodiments furthercomprise an auxiliary stator winding 1262 whose field is oriented at anangle (e.g., 45° to 135°) with respect to the stator windings. Thisfield may be energized at startup (e.g., via 1540 or 1550) to produce anunconditional torque on the rotor windings. The energization of 1262 maybe removed or changed depending on the rotation rate of the rotor orline parameter.

Some alternative embodiments comprise a three-phase motor/generator,which may not require an auxiliary winding to ensure that a start-uptorque is applied.

At synchronous rotation, windings on the rotor of the two-phasemotor/generator experience an oscillating magnetic field component attwice the line frequency produced by currents in the primary statorwindings. In addition, the rotor may experience a field induced by anauxiliary stator winding. If an auxiliary winding current issubstantially DC, a rotor winding experiences a magnetic fieldoscillating at the line frequency. Some embodiments use an AC componentof the current in an auxiliary stator winding at a non-line frequency.In some embodiments, an auxiliary rotor winding is in electricalcommunication with circuity that extracts power from the induced voltageand current.

In some embodiments a part of that power extraction circuitry is arectifier, a half-bridge rectifier, a full-bridge rectifier, or atotem-pole synchronous rectifier. In some embodiments a part of thiscircuitry is a regulator of voltage or current. In some embodiments theregulator has an adjustable threshold. Some regulators comprise aswitching converter. Some embodiments utilize a voltage comparatorcircuit in part to determine switch timing. In some embodiments, thecomparator compares a reference voltage with a voltage derived from oneor a combination of: the output voltage of the circuit, the outputcurrent of the circuit, an analog signal from an auxiliary winding, ademodulated analog signal, or a sensor. In some embodiments thereference voltage is fixed, while in others it may be adjusted by acontroller. Some embodiments comprise feedback wherein the feedbackcircuit regulates the power factor of the generator via adjusting howthe field winding is energized.

In some embodiments, the field-winding current or applied voltage isregulated by adjusting the current or voltage applied to an auxiliarywinding of the stator, and the induced current in the auxiliary windingof the rotor is rectified as described previously and the resultingvoltage waveform or low-pass-filtered waveform applied across the fieldwinding to produce the field current.

Some embodiments obviate a rotor microcontroller by providing forindirect control of the field winding energy via astator-reference-frame controller that supplies a waveform to at leastone stator winding. In some embodiments the waveform is substantiallyDC, substantially near line frequency, or substantially above linefrequency.

Some rotor electronics comprise a frequency selective filter on a rotorwinding. Some embodiments obviate an auxiliary rotor winding byfrequency multiplexing operations of a rotor winding.

Some rotor electronics comprise at least one winding on a distinctmagnetic circuit from the field windings. Some embodiments couple powerto at least one rotor winding using a magnetic field having asubstantial axial component.

Some rotor electronics receive power used to supply the field windingfrom an alternative source, e.g., a rotating battery, coupledphotovoltaic cells, an electrostatic coupling, etc.

Non-Rotary (Stator-Frame) Electronics

Some embodiments comprise stator electronics 1220 that perform one ormore of: communicating with a second controller, optically measuringflywheel position from fiducials and indicia, measuring generator shaftangle (e.g., optically, via a sensor including a rotary encoder,hall-effect sensor, etc.), measuring instantaneous stator-windingparameters (e.g., currents, voltage, power, voltage error, temperature,vibration offset, vibration force, acceleration, IR temperature),free-space optical communications, wireless communications, control ofthe voltage and current in at least one stator auxiliary winding, analogto digital conversion, digital to analog conversion, pulse-widthmodulation, battery charge control, interlock monitoring, performancemonitoring, data reporting, data logging, variable-frequency motordrive, or AC inversion.

Some non-rotary electronics perform load management as described above.

Some functionality of the stator-frame electronics may be physicallyconnected to the motor/generator apparatus, such as shaft encoders,optical sensors, optical communications, etc.

Some embodiments package some functionality of the non-rotaryelectronics into a removable or re-positionable module, e.g., in housing1502. For example, some embodiments combine battery charge control andmotor control electronics in a removable package that is connected by aplurality of breakable electrical connections 1504, that on removalchanges functionality over to one or more standard AC sinewave inverters(1530, 1540) connected to one or more outlets (1560, 1562) and batterycharge controller (1510, 1516, 1520). Some embodiments further allow theremoved module to be plugged into a wall outlet to charge the batterypack. Some embodiments further allow the removed module to be pluggedinto an automotive “cigarette lighter” connector (1584) to allowrecharging even if the AC grid is unavailable.

Some embodiments include additional functionality that is useful in anemergency, such as one or more of a light (1586), a radio (1588), a 12-Vbattery charger (1580/1584), a USB charger (1580/1582), etc.

In some embodiments, when the power from solar panels is no longersufficient to power household loads, the system automaticallyregeneratively breaks the flywheel, supplying charge to its batteries.It may then be disconnected from the motor/generator connector and movedto a convenient location for supplying limited overnight spot power. Inthe morning, it can be reconnected to the motor/generator connector andreinitiate the system startup procedure.

Conventional PV inverters may generally fall into two categories:grid-tied or non-islanding inverters and off-grid or islandinginverters. Both types of inverters are substantially limited in thesurge power they can provide because the average output power is limitedby the photon flux on the PV panel or panels at their input and theinverters generally have little on-board bulk energy storage. Someinverters comprise a bulk storage (e.g., battery) element that cansupplement the PV source power when needed. This energy may flow throughthe same circuit that carries the PV energy or through additionalcircuitry. Either way adding substantial surge capacity increases thecost of the inverter.

Increasingly, battery backup systems, comprising a battery-fed inverter,are used to create a microgrid during an outage. The surge capacity ofthese systems may be limited by battery capacity or amount of activematerial in the batteries or desired service life of the batteries.Adding a three-times surge capacity to a battery system requires one ormore of: the use of more expensive high-discharge batteries, a reductionin the service life of the batteries, or a corresponding increase in theamount of active material in the batteries, all of which decrease theeconomy of the battery system. In addition, the inverter tied to thebattery must be rated for the surge power, compounding the system cost.

Some embodiments overcome this problem by substantially eliminatingsurge-power requirements for the battery or inverter components of amicrogrid. Some embodiments may comprise a generator/alternator, aflywheel, an inverter and dump load controller herein called an “agent,”and a generator motion controller. The combination works as a miniature“synchronous condenser” to create and stabilize the voltage waveformand, in some embodiments, power factor in a microgrid. The generator maybe sized affordably to have a low effective output resistance (e.g.,0.5Ω for a 10-kW generator) so that an instantaneous current surge of 80A, produced, e.g., by the start of a vacuum cleaner, air conditioner, orpower tool, produces a momentary Voltage dip of ˜17% in the microgrid of(40 V out of 240 VRMS), which may be tolerable for the vast majority ofhousehold and industrial loads. The mass of active material in such agenerator, mostly steel and copper or aluminum, may be roughly 32 kg,and the volume of the active element may be approximately 0.007 m3. Thecommodity cost and size requirements of the generator material comparesfavorably to the corresponding costs for present-day-technology chemicalstorage batteries. Of course, the additional active battery materialadds capacity, but the value of this capacity diminishes if it farexceeds the needs for average load power.

FIG. 2A shows a front-side view 2000 of an exemplary microgrid systemcontroller with a front cover removed according to an embodiment.Element 2002 is an AC generator. Element 2020 comprises in part avariable frequency drive to start the motion of the generator. Element2024 is a controller board herein called an “agent” used to manage thevoltage waveform experienced by a connected inverter. Element 2012 is anexhaust air duct and element 2014 is a duct-based resistive heater usedto dissipate surplus energy from an inverter.

Airflow Control

Some embodiments seek to take advantage of air motion induced by theflywheel to enhance the cooling performance of one or more of:electronics, generator, bearings, or heat dump heater. In the embodimentof FIG. 2A, element 2008 is an array of negative-pressure (inlet) holespositioned so incoming air passes over cooling fins on the circuits 2020and 2024. In some alternative embodiments a circuit is cooled by apositive pressure induced by the flywheel. The flow lines 2026 representthe route of air into the unit, over electronics and into the generatorbody. Element 2006 is an air duct from the air exit of the generatorinto the flywheel cavity whose outer front is surface 2010. Flow line2027 depicts the route of air from the generator into this cavity.Element 2013 is the exhaust port of the flywheel cavity. This port feedsforced air through heater 2014 and ductwork 2012 along the flowlinesdepicted by 2028.

Some embodiments further comprise element 2029, a thermally conductiveplate disposed on the wall of the flywheel cavity 2010. In someembodiments, the thermally conductive plate extends to comprise more orall of 2010. The opposite surface of 2029 is exposed to flywheel-inducedrecirculating airflow. Some embodiments employ this plate as a coldplate or heat sink for at least one power electronic component.

FIG. 2B shows a side view 2030 of an exemplary microgrid systemcontroller according to an embodiment. Element 2032 is an exhaust airvent. In some embodiments, this vent may be steered. In someembodiments, this vent cover can be removed or swung open revealing aconnector for a detachable flexible vent hose, such as a dryer hose. Insome embodiments, a cavity behind the vent cover provides storage for acollapsed segment of high-temperature air hose. In some embodiments thisallows dump heat to be routed for best effect, e.g., for drying orheating or to dump unwanted waste heat where it is not a nuisance.

FIG. 2C shows a back-side view 2040 of an exemplary microgrid systemcontroller with central and front covers removed according to anembodiment. Element 2042 comprises the back cover and the rear outersurface of the flywheel cavity. In some embodiments, the flywheel-facingsurface is substantially smooth and streamlined to reduce aerodynamicdrag. Element 2044 is the exit cavity of the duct 2012.

FIG. 2D shows a back view 2050 of an exemplary microgrid systemcontroller with a back cover removed according to an embodiment. Element2052 is a flywheel. In some embodiments the flywheel comprises one ormore sheets or plates of steel that is stamped, cut, or machined into anaxisymmetric shape. In some embodiments, the flywheel may comprise astack (2054) of multiple cut parts. This may facilitate installationover a single heavy flywheel. It may further simplify adding or removingflywheel storage capacity. Elements 2056 are holes for bolts that holdthe flywheels firmly to a flange. In some embodiments, these holes areslightly oversized so that the bolts do not substantially resist anyoutward deflection of the flywheel under centripetal loading. In someembodiments, the hub shaft 2058 fits the central hole of 2052 with asubstantially tight tolerance, e.g., 0.05-0.5 mm. In some embodiments,this shaft provides the primary radial force that centers the flywheel.In some embodiments, the flywheel is waterjet cut to net shape. In someembodiments, an outer surface of the flywheel may be smoothed orpolished to reduce aerodynamic drag.

FIG. 2E shows an alternative back view 2060 of an exemplary microgridsystem controller with a flywheel 2052 removed according to anembodiment. Element 2006 is the air inlet cowling from the generator andelement 2013 is exhaust duct of the flywheel cavity. In some embodimentsan aerodynamic vane 2064 may be used to augment the flywheel-inducedflow through the exhaust. In some embodiments an actuator 2066 may beused to regulate or adjust the flow through the exhaust. In someembodiments this flow control is used in concert with the heat dump tomaintain a desired out-flow or case temperature. Some alternativeembodiments employ a variable obstruction that changes the flow area of2013. Elements 2068 represent the gradual outward spiral of the flywheelinduced flow. The relatively wide cavity around streamline 2070 mayreduce aerodynamic drag losses. Streamline 2072 represents the outflowpath. Element 2076 is the flywheel mounting flange/hub which in someembodiments is affixed to the generator shaft strongly enough to resistpulling off the shaft under any flywheel fault condition. In someembodiments, this flange locks into a mechanical détente, groove, orshoulder of the shaft. In some embodiments, this flange is welded to theshaft. In some embodiments this flange is held to the shaft with atleast one high-strength pin.

Element 2029 is the side of the cooling plate exposed to inducedairflow. In some embodiments, this plate may further comprise surfacefeatures to increase the wetted area. In some embodiments, a surfacefeature of 2029 may be substantially aligned in the circumferential flowdirection.

FIGS. 2F-2J show alternative arrangements of the power dump and coolingair vents according to some embodiments. Some embodiments comprise ahousing element 2102 designed to prevent ingress of standing water. Someembodiments further comprise one or more housing elements 2104 designedto shed rain water. Some embodiments further comprise an element orelements 2106 designed to prevent ingress from splashes, insects,animal, fingers and the like such as a screen, a hydrophobic mesh, etc.Such elements may facilitate the use in hurricane or flood disasterrecovery or use outdoors. Elements 2108 and 2110 are respectively theair inlet ports and air exit ports.

FIG. 2F shows an arrangement 2100 comprising a plurality of inlet portsaccording to an embodiment. The exit port may comprise a flap 2112. Inthis embodiment, element 2114 is a hose connector. Element 2116 is afixed or detachable flexible hose that may be used to position theexhaust heat.

FIG. 2G shows an arrangement 2200 comprising an inlet port and an exitport on opposite sides of the device according to an embodiment. Such anarrangement may help to prevent re-ingestion of exhaust air.

FIG. 2H shows an arrangement 2300 comprising an inlet located proximallyto the generator air inlet according to an embodiment.

FIG. 2I shows an arrangement 2400 comprising a plurality of air exitsaccording to an embodiment.

FIG. 2J shows an arrangement 2500 that houses the active power dumpoutside a substantially water- and air-tight housing 2502 according toan embodiment. Element 2504 is an electrical cable carrying power andcontrol lines. Element 2506 comprises a load and load housing. In someembodiments, element 2506 further comprises a fan. Some such embodimentsmay eliminate an internal cowling (2010) allowing the fly-wheel-inducedair to circulate throughout the interior of the housed system. Such anarrangement may spread internally generated heat for better naturalconvection from the outer surface of 2502.

In some embodiments an element of the outer housing is made of athermally conductive material. Such an arrangement may enhance removalof heat from the interior of the system. In some embodiments an elementof the outer housing comprises an insulating material. Such anarrangement may prevent burns from contact. Some embodiments maycomprise both thermally conductive elements and insulating elements toprovide both efficient cooling and safety from burns. In someembodiments the housing may comprise a metal shell with a perforated,slotted, meshed, screened, or otherwise disposed outer insulator thatkeeps fingers away from heated surfaces, but facilitates airflow.

FIG. 3 shows a view 3000 of an interior of an exemplary microgrid systemcontroller having a ducted heater 2014. Element 3002 represents theoutside extent of a coil of a heating element, e.g., a nichrome wire.Element 3004 is a ceramic or other high-temperature insulating standofffrom the internal frame 3006. This frame structure may be substantiallyflow aligned to reduce back pressure or aerodynamic losses. Element 3008is a dump load switch circuit. Some embodiments further comprisemetallic or screen, mesh, perforated plate, etc. at the entrance andexit of the heater 3010 to contain electromagnetic emissions that mayotherwise radiate resulting from PWM-ing or otherwise modulating aswitch in circuit 3008. Some circuits 3008 employ substantiallyconstant-on-time switching, which may confer faster time response andmay help to eliminate excessively short switching pulses at low dutycycles. In some embodiments, the constant on-time may be adjusteddynamically for power conditions. In some embodiments, the controllermay change switch driving modes in different parts of the AC cycle. Forexample, the controller may aggressively enforce zero-crossing times byswitching full on or near full on, whether the voltage waveform is outof specification or not. This may help to satisfy a PV inverter that isprobing the grid signal by perturbations.

Some embodiments comprise a second, in some cases low-pass-filtered dumpcircuit which can be wired or plugged into an appropriate load. Someembodiments comprise a water heater circuit similar to an instant hotwater heater. Some embodiments may employ a limited amount of waterheating in normal operation or as a thermal fail-safe.

Electrical Connections

Some embodiments comprise a unit having one or more of: an AC connectionto an output of a PV inverter, an AC connection to a circuit breakerrated appropriately for a PV inverter on an electrical panel, or an ACconnection to a circuit breaker rated appropriately for a generator onan electrical panel.

Some embodiments further comprise an actuatable switch ratedappropriately for a generator. In some embodiments, this switch maycomprise one or more of a thyratron, SCR, MOSFET, IGBT, transistor, oran arrangement thereof, a solid-state relay, a mechanical relay, acontactor, or a manual switch. In some embodiments, this switch isactuated by a controller circuit in the unit. In some embodiments theswitch is manually controlled. Some embodiments employ a circuit breakerin lieu of this switch.

Agent Controller

The agent module (2024) may comprise power switching circuitry to do oneon more of: apply a load to the inverter output, isolate the inverterfrom a load, or apply power to an inverter output. The role of the agentmay be to manage these loads.

A second role of the agent may be to provide protection for loadsconnected to the external electrical panel, herein called “microgridloads.” In some embodiments, while the generator is connected to theexternal electrical panel its low output impedance provides damping ofvoltage transients. However, when the generator is disconnected from themicrogrid (e.g., during a microgrid blackout) this protection is notpresent.

Continuous Overvoltage Protection

In some embodiments, some agent circuitry remains connected to theelectrical panel/loads even during a microgrid blackout, for example, anovervoltage power dump used to protect devices connected to theelectrical panel from inductive spikes, spurious generated voltagesources such as induction motors, or other faults. Some embodimentscomprise a metal oxide varistor or other such powerline protectiondevice. Some embodiments may comprise a protection module as shown inFIG. 4A, which is a schematic view 4000 of a passive overvoltage powerdump according to an embodiment. In circuit 4000, two AC circuits 4002are full-wave rectified by 4004 producing a positive voltage differencebetween 4006 and 4007 that is substantially proportional to the absolutevalue of the peak voltage between inputs 4002. Element 4008 is anavalanche or Zener diode having an appropriate reverse breakdown voltagesuch that when the voltage 4006 to 4007 exceeds a threshold, in someembodiments, current flows through diode 4008 through conductor 4009into the gate of switch 4010, raising the gate voltage to a value thatmay be limited by Zener diode 4012, e.g., having a 6 to 20 V reversebreakdown voltage. Some embodiments of 4010 comprise a MOSFET, IGBT,etc. Some embodiments may further comprise a current-limiting resistorin this diode circuit, however this may increase the actuation delay ofswitch 4010 and affect the performance in protecting against fasttransients.

When the gate voltage of switch 4010 exceeds a threshold, it turns onproviding a low resistance path between 4006 and 4007 through powerresistor/heating element 4014. A snubbing network 4016 may provide acurrent path for intentional or parasitic inductance of load 4014 todissipate without producing a voltage spike across switch 4010 whenturning off

Circuit elements 4013 and 4012 are intended to tailor the turn-on andturn-off dynamics of switch 4010. It may be desirable to operate theswitch substantially in its fully saturated gate state to avoidexcessive heat generation in the switch. In some embodiments, the gatecircuit contains a nonlinear element 4016, such as a voltage supervisoror under-voltage lockout circuit, to prevent out of saturation behavior.Some such embodiments may further comprise circuitry to accept a secondinput, e.g., a digital switch signal 4018. Some such embodiments maycomprise circuitry to perform logic such as an ‘or’ operation on asecond input with the primary input in setting the switch-gate state.Some embodiments may comprise an input 4020 that is an analog signal.Some such embodiments may comprise logic and a comparator functionbetween the primary and secondary input to determine the switch-gatestate.

Some fast overvoltage protection embodiments comprise protection betweensingle-phase circuits L1 and L2 (applied across 4002). Some embodimentscomprise protection between single-phase circuits L1 to N (appliedacross 4002 of one circuit) and L2 to N (applied across 4002 of a secondcircuit). Some embodiments provide capacitive isolation to at least oneAC line, allowing the two single-phase circuits driving separate bridges4004 to share the same switch circuit and load.

Inverter Voltage Limiting

As used herein, the phrase ‘tripping the inverter’ refers to applying anout-of-specification voltage waveform to an inverter that causes theinverter to pause output or shut down, herein called ‘tripping.’ Anobjective of the agent controller may be to prevent the inverter fromtripping over the widest practical envelope of load applications. Asused herein, the phrase derating inverter output' refers to an inverteroperating below the maximum power point because of a frequency, voltageamplitude, or instantaneous voltage excursion past a nominal setting,e.g., ‘voltage-frequency control.’

Some agent controllers comprise circuitry to ensure the inverterexperiences only in-specification voltage waveforms that preventinverter tripping while the apparatuses described herein are operating.An ‘in-specification voltage waveform’ may comprise minimum and maximumsinusoidal voltage amplitudes and frequencies and instantaneous voltagesthat may be fixed, linked to each other, set programmatically, or setvia non-volatile memory settings according to a configuration. As usedherein a ‘voltage envelope’ comprises the instantaneous minimum andmaximum allowable voltages and may further comprise other instantaneousthresholds.

Envelopes or threshold may similarly apply to other sensed parameters,such as current and temperature. For example, an agent in agrid-connected unit may enforce a “no-power-export” requirement orotherwise limit power export via such an envelope. These envelopes maydepend in real time on measurements, e.g., a current envelope may bereduced when the temperature is high.

Some embodiments contain circuitry to ensure the inverter experiencesonly voltage waveforms that support its nominal output, so that theinverter can operate substantially at the maximum power point setting ofthe solar array. Some embodiments relax the maximum voltage or frequencyspecifications to allow an inverter to derate its output by a fixed orprogrammable amount, a fixed or programmable fraction of output, or acombination. Some embodiments adaptively change at least one envelopesetting according to measurements of one or more of production, load,time-of-day, or temperature. Some embodiments change at least oneenvelope setting according to external commands, e.g., from ahome-automation system.

Some agent controllers control at least one agile load dump circuit.FIG. 4B shows a schematic diagram 4030 of an embodiment of such acircuit. Its operation is identical to that of the overvoltageprotection circuit FIG. 4A, except that the gate signal 4032 is applied(in some embodiments through voltage isolation) by the agent controllerinstead of leakage through an avalanche diode.

In some embodiments a microcontroller performs calculations to establishnumerical values related to the voltage envelope according to aconfiguration. In some embodiments, this configuration or thiscalculation employs a ‘derating factor’ that reduces the allowable rangefrom the inverter's limits to prevent measurement error orline-impedance effects from tripping the inverter or to providetolerance for control-loop lag, hysteresis or perturbations used in theinternal workings of the agent's power circuitry. In some embodiments, amicrocontroller discretizes the voltage envelope into ‘lookup tables’ ofnumeric entries representing the instantaneous voltage minimum andmaximum limits. In some embodiments, these lookup-table settings aredynamically updated by a control system or in response to a digitalcommand. The use of such lookup tables may facilitate efficient updatesof real-time parameters in high-speed interrupt service routines.

In some embodiments, a microcontroller maintains a model of an idealinstantaneous voltage, phase, and voltage amplitude, herein called a‘target’ to apply to the inverter. In some embodiments, this model isderived from one or more of: repeated analog to digital conversion,analog comparison, zero-crossing detection, digital handshaking lines toa second controller, digital communication lines, analog handshakinglines from a second controller, or an analog waveform.

In some embodiments, a microcontroller generates one or more analogvoltage waveforms related to the instantaneous voltage envelope at thetarget phase, herein called ‘inverter voltage limit signals’ (IVLS). Insome embodiments this generation employs a digital-to-analog converter(DAC) peripheral. In some alternative embodiments, this generationemploys a filtered pulse-width modulated (PWM) waveform with duecompensation of phase lag of the filter.

In some embodiments, at least one analog comparator compares an analogsignal, herein called the ‘inverter voltage monitor signal’ (IVMS),derived from the actual inverter voltage by one or more of: resistivedivision, filtering, level shifting, or phase shifting, with an IVLS toproduce a digital signal that changes state when a limit threshold isexceeded. In some embodiments, this digital signal may trigger one ormore of: a switch, an interrupt, a timer, a counter, or a gate. In somealternative embodiments, a comparator generates an output based on thecomparison of the sum or difference of IVMS and IVLS with a fixedvoltage reference, including 0 V.

Some embodiments comprise a further signal, herein called a ‘switchcoordinator signal’ (SCS) comprising a periodic perturbation signal,such as a triangle waveform at a preferred switch frequency. In someembodiments the SCS frequency lies between 4 kHz and 1 MHz andpreferably between 25 kHz and 250 kHz. In some embodiments this signalis summed or differenced with the IVLS or IVMS. In some embodiments thissignal is summed or differenced with the difference between the IVLS andIVMS. In some embodiments this perturbation signal has a hystereticeffect that favors the establishment of switching at a desiredfrequency.

Some embodiments employ a weak positive feedback signal from the outputof the comparator to the input to effect hysteresis that may have theeffect of limiting the maximum switching frequency.

Some embodiments comprise a digital switch-duration limiter. Someembodiments comprise a monostable timing circuit. Some embodimentscomprise a counter circuit. Some embodiments allow real-timeprogrammatic control of the switch duration.

Some embodiments perform rapid analog to digital conversion of a IVMSand digitally compares the instantaneous reading with one or moreinstantaneous limits. In some embodiments an excursion past a limit mayprompt an immediate response, e.g., an abrupt increase or decrease in aPWM duty cycle or an abrupt change in switch state. In some embodimentsthis change may be relaxed after a subsequent measurement lies withinthe instantaneous limits.

An abrupt excursion may be caused by an inrush current to capacitors, amotor start, the actuation of a switch on a heavily loaded circuit,cycling on and off of a main load like an oven, etc. In someembodiments, the agent circuitry and firmware have sufficiently hightime response to maintain the inverter voltage within the envelope,whatever transient loads appear or disappear. To this end, higherswitching frequencies, and higher sampling rates, may be preferred. Atypical response time of a comparator may be in the range ns-μs. Atypical A/D sampling period may be 4 μs-50 μs. A typical PWM period maybe 5 μs-50 μs. The inductance of a filter inductor to smooth the switcheffect may be judiciously low enough to provide sufficiently highresponsivity. In some embodiments, filter capacitors may slow the rateof excursion.

Some agent controllers comprise a closed-loop controller. Someclosed-loop controllers adjust the value of a duty-cycle parameteraccording to a combination of one or more of: the instantaneous errorsignal between an IVMS and a target, (discrete) nth-order timederivatives thereof, nth-order integrals thereof, the instantaneouserror signal between an IVMS and a limit, (discrete) nth-order timederivatives thereof, or nth-order integrals thereof. Some control loopschange a least one parameter used in the calculation of a duty cycledepending on an operating state variable. This operating state variablemay be changed by high-speed interrupt service routines used to detectexcursions past limits.

In some embodiments, if the instantaneous inverter voltage error tendstoward excessively high voltage (positive or negative) the controllerincreases the amount of power dumped. In some embodiments this actioncomprises turning on or increasing the duty cycle of a switch in anagile dump circuit.

In some embodiments, if the instantaneous voltage excursion is towardlow-voltage (too close to 0 V), the dump power is reduced, e.g., byreducing or zeroing the duty cycle of the power-dump circuit switch. Ifthe low-voltage state is severe, e.g., passes the instantaneous limits,the agent may open an agile isolator circuit between the inverter andmicrogrid load, momentarily powering the entire microgrid from theflywheel generator. This kind of situation may arise when a high surgeload is applied to a microgrid. For example, the surge current to starta rotary power tool may instantaneously exceed 80 A. If the flywheelgenerator has an output impedance of 0.5Ω, the microgrid voltageinstantaneously drops by 40 V, ˜17% of the nominal RMS value. This surgedecays rapidly over several AC cycles. This level of perturbation to themicrogrid may have minimal or no effect on other microgrid loads, but issufficient to trip the inverter. Legacy PV inverters will trip and notresume power production for long enough that the microgrid will blackout (without a secondary source of power, such as a battery inverter).PV inverters with ride-through capabilities will trip for a number ofcycles or seconds, then restore power. However, the seconds of lostpower production could still lead to a microgrid blackout.

While the isolator circuit is open, the agent may stabilize the inverterwaveform by actively controlling the dump circuit.

FIG. 4C shows a schematic diagram 4050 of an embodiment of a fastisolator circuit according to an embodiment. The agent actively controlsthe voltage 4052, in some embodiments through an isolated gate drivercircuit. The circuit 4054 may tailor the turn-on and turn-off dynamicsof the isolator for smoother, low transient isolation and re-connection.Switches 4056 may comprise MOSFETS, IGBT, transistors, etc. They mayalso comprise thyristors or SCRs, but this may defeat some of theagility of operation e.g., if isolation is only needed during a fractionof an AC cycle. When the voltage 4052 is above a threshold, switches4056 conduct bi-directionally with low resistance, connecting 4058 and4060. When the applied voltage is below a threshold, switches 4056 arehigh resistance and do not substantially conduct bidirectionally. Thecircuit elements 4062 are intended to smooth and absorb transients thatoccur during switching. While the switches 4056 are non-conducting, 4062weakly capacitively couples 4058 and 4060, but not enough to drive theinverter voltage below its limits. In some embodiments, one of the L1and L2 lines is isolated. In some embodiments, such as when an inverterhas an active neutral, two lines (e.g., L1 and L2, L1 and N, or L2 andN) may need to be isolated.

Microgrid Reserve Capacity

In some embodiments, a controller monitors the load current and the PVinverter production capacity. In some embodiments, the controller learnsthe excess production capacity by measuring or inferring from a switchduty cycle the amount of power it must dump to a load to keep thevoltage waveform in specifications. In some embodiments, the microgridsystem controller periodically or occasionally ramps its dump power todetermine the PV inverter capacity. In some embodiments, the controllermeasures the current from the PV inverter.

In some embodiments, the microgrid system controller controls its dumpcircuit so that the PV inverter operates substantially at the maximumpower point of the photovoltaic array. In some embodiments, this mayhave the benefit of providing the maximum responsivity to surge loads.The rate at which a PV inverter can slew its output power and determinemaximum power point may be practically and regulatorily limited (e.g.,to 10-1-102 s), whereas the controller may reduce its dump load powerrapidly (e.g., in 10-6-10-3 s). By rapidly shedding dump power, thecontroller may help to handle fast surges in a time frame that themechanical response of the flywheel generator (e.g., 10-3-10-2 s)cannot.

If the dump power is used productively, e.g., for heating, drying,cooking, cooling, dehumidifying, process power, battery charging, waterpumping, electrolysis, etc., it may be advantageous to operate the dumpso that the PV inverter always produces substantially maximal power. Ifexcessive dump power is problematic, e.g., produces excessivetemperatures or overpowers a process, etc., it may be advantageous tooperate at a lower inverter power, while maintaining a reducedfast-reserve capacity.

In some embodiments, a controller wirelessly signals one or morereceivers in response to changes in the reserve capacity. For example, atransition to a low-reserve state may be announced via a wirelesstransmission or broadcast to one or more of: a smart phone, a homeautomation controller, a computer, a WIFI access point, a Bluetoothdevice, a Bluetooth low energy device, a Zigbee device, or a radioreceiver or transceiver. This announcement may help a homeowner quicklyswitch off an appliance or load that they recently added. For example,turning on an electric range may overload the system. Within a second, abeeping on a phone may alert the person using the appliance that it istaking too much power giving the person time to turn off the overloadbefore there is a blackout.

Remote Alerts and Control

The unit may report instantaneous reserve-capacity readings which may bedisplayed in a variety of formats including images or icons of devicesthat can be turned on without risking a blackout. In some embodiments,devices may be color coded depending on their risk factor, e.g., grayedout, invisible, or removed from a list may mean a device can definitelynot be powered.

Red may mean a device may risk a blackout, yellow may mean adding thedevice will bring the reserve capacity below a desired minimumthreshold, green may indicate no problem. In some embodiments, thecontroller communicates with a smart appliance/smart home server ordirectly with smart home devices on a priority system. In someembodiments, a user may click an item to add before turning on thatitem. This selection may be communicated to a controller which may takedirect or indirect actions to shed loads or add microgrid capacity toaccommodate the request. The state of success of these actions may becommunicated to a remote device producing a visual, audio, or tactilefeedback that indicates that it is safe to add the load or not.

Microgrid Blackout

In some embodiments, a microgrid blackout may be triggered when acontroller senses that the applied loads are unsustainable, e.g., thereserve capacity is less than or equal to 0 or a minimum thresholdvalue. In some embodiments, the controller opens the load circuit via asolid-state relay or other fast acting semiconductor switch circuit. Insome embodiments switching is preferably performed at a zero-current orzero-voltage state part of the AC cycle. In some embodiments thecontroller opens a contactor or breaker between the generator andelectrical panel/loads.

In some embodiments, during a blackout, the apparatuses described hereinkeep the inverters productive and maintains the flywheel rotation, etc.In some embodiments, a user may remotely request the apparatuses toretry powering the microgrid by, e.g., touching a button on a smartphone, etc. In some embodiments, the apparatuses may automatically retryestablishing the microgrid when its flywheel is spun up to fullcapacity.

Energizing the Flywheel Generator

Some generators comprise a brushless design with a split rotor windingwith opposing diode rectifiers and a stator comprising a split mainwinding and an auxiliary winding feeding a capacitor. Some embodimentsfurther comprise one or more damper windings on the rotor. Such agenerator may be self-started by use of a single-phasevariable-frequency drive (VFD) circuit, behaving qualitatively similarto an AC induction motor until it locks into synchronous rotation. Anadvantage of the use of a single-phase VFD is a reduction in circuitcomplexity and an improved ability to utilize stators having differentturns ratios in the primary and secondary. In some embodiments shaft orflywheel angle feedback may be merited to optimize the spin-up time,energy, and reliability. Some alternative embodiments comprise aseparate VFD phase on the main winding and on the secondary winding.

Some generators comprise a brushed design with a substantially DCcurrent in the rotor winding, transmitted across brushes. Advantages ofthis arrangement may be an improved regulation of output voltage, and animproved ability to sink and source variable reactive power. Such agenerator may require an auxiliary stator winding to ensure startup froman arbitrary shaft angle. With a brushed design, there is an increasedlikelihood of an insulating film produced by corrosion or oxidationbetween the brush and the rotor contact. In some embodiments, such aninsulative layer may be disrupted by applying a momentary high voltage,applying across the brushes a momentary AC or radio-frequency pulsetrain with or without a DC component.

Some generators comprise a brushless design employing a claw rotor witha non-rotating solenoid at its center. This arrangement may have thebenefit of good voltage regulation and reactive power (VAR) control of abrushed design without some of the complications of brushes. A cost maybe an increase in leakage inductance.

Some generators comprise a permanent magnet on the rotor. In someembodiments, this permanent magnet field augments an armature windingfield.

External Flywheel Generator Starter Mechanism

Some embodiments obviate a secondary winding by the use of an externalforcing mechanism. In some embodiments the forcing mechanism is one of:a motor, a brushless DC motor, a brushed DC motor, a stepper motor, oran induction motor. In some embodiments, the forcing mechanism is one ofa solenoid actuator, a spring, a solenoid-actuated spring release. Insome embodiments, flywheel/rotor motion is initiated by actuating asolenoid that imparts a circumferential force on the flywheel, shaft, orrotor. In some embodiments, this motion may scrape a clean contact forbrushes. In some embodiments, the actuator impulse is designed toproduce enough motion to rotate a rotor that has stopped in a positionwhere the stator winding field does not produce a substantial torque toa position suitable for starting by energizing a primary stator winding.

In some embodiments, an external forcing mechanism obviates an auxiliarystator winding. In some embodiment, the solenoid may be actuatedrepeatedly so that its impulse to the flywheel can be a multiple of thesingle actuator impulse.

In some embodiments an external starter mechanism may be employed innormal operation to add power to or draw excess power from the flywheel.Such a mechanism may provide a simple means to add DC-side batterybackup capabilities, by feeding power to the flywheel generator throughthe starter mechanism using regulated battery power.

An alternative flywheel generator starter mechanism may be afuel-burning engine. The engine may be started to energize the flywheel, then electromechanically decoupled until it is needed to provideadditional power. Such an arrangement may provide substantial night-timepower capacity while saving on fuel costs during the day.

In some embodiments electrical power to energize the flywheel generatorcomes substantially from the PV inverter. Because the PV inverter mayrequire a carefully shaped voltage waveform, it may be important to usea power-factor control circuit in the formation of a substantially DCsupply to feed a VFD circuit. In some alternative embodiments, thefast-dump circuitry agilely compensates for a lack of or imperfect powerfactor control on the VFD power supply.

Some VFD controllers comprise a DC supply that can dynamically vary itsoutput during the energizing process. Some VFD controllers comprise alow-voltage, high current power supply, in some cases supplied by abattery, to provide the high-current low-voltage waveforms needed duringthe early startup of the generator. Such voltage sources may be “or-ed”together using switches or diodes. Some controllers may switch aparallel and series arrangement of a power source such as batteries,transformer windings, motor windings, etc. A motor generator maycomprise a centrifugal switch.

FIG. 5A shows a microgrid system controller 5000 and its externalcontext according to an embodiment, including the PV system, external PVinverter (1004), electrical panel (1006), and an optional gridconnection (1005). Elements 5008 represent the physical connectionbetween external and internal wiring and may comprise terminal blocks,swage connections, or other line-voltage connections. In thisembodiment, current from the PV inverter output flows through conductorelement 5010. Some embodiments comprise a second conductor element 5012that connects to a circuit breaker 5006 on an electrical panel. Attimes, element 5012 conducts current from the PV inverter to theelectrical panel. Some embodiments may further comprise a connection5014 that connects to a circuit breaker 5002 on an electrical panel. Attimes, element 5014 conducts current from the generator 1200 to theelectrical panel. In some embodiments, having two separate outputs tothe subpanel can independently protect against inverter overloads andgenerator overloads, which may require substantially different currenttrip points. Some alternative embodiments comprise an internal circuitbreaker 5015 between connection 5013 and 5014, obviating connection5012. Such an arrangement may have the advantage of a simplerinstallation process. A retrofit installation may already comprise thePV inverter breaker and wiring, allowing the system 5000 to be spiced into existing circuitry.

Element 5004 is an interlock that prevents the simultaneous closure ofthe generator breaker 5002 and a main switch, e.g., a service disconnect1010. In this embodiment it is a mechanical interlock that physicallyinterferes with closing both switches simultaneously. Some alternativeembodiments may comprise an alternative interlocking scheme or manual orautomatic transfer switch to ensure the generator cannot back-feed powerto the grid. Some embodiments allow the generator to back-feed the gridand either do not have an interlock or can disable the interlock.

Element 5016 is an actuatable switch, e.g., a relay or other switch asherein defined. In one state, the switch may short-circuit 5010 and 5012so the current from the PV inverter can flow to the subpanel. In theother state, the switch may short-circuit 5010 and connection 5032herein called the ‘regulated bus.’

Element 5018 is an agile power dump circuit like that in FIG. 4A or FIG.4B, or another switch as defined herein. When actuated, it connects theregulated bus to a load 1574, e.g., a substantially resistive load inthe 100's of Watts to 10's of kW range, and preferably in the rangewhere this load can dissipate power comparable to or greater than thecapacity of the solar array.

Element 5020 is a second actuatable switch, e.g., a fast isolator suchas that in FIG. 4C, or another switch as herein defined. In someembodiments, this switch is used to interrupt current from the regulatedbus to the subpanel, e.g., during an overload event to prevent theinverter from turning off its output.

Element 5022 is one or more actuatable switch, e.g., a relay, fastisolator circuit or other switch as herein defined, that individuallyconnects the regulated bus to a user-configurable load via a connection5024. These switches may allow excess power in the regulated bus to beapplied to a load other than load 1574.

Element 5026 is an actuatable switch as defined herein that can connecta battery and charge controller module 1520 with the regulated bus.

In this embodiment, 1520 can supply power to a variable-frequency drive(VFD) inverter 1540. Actuatable switch 5030 is a relay or other switchas defined herein between the output of the VFD and regulated bus in oneposition and the output of the VFD and at least one winding of thegenerator 1200.

In this embodiment, element 5034 is a relay or other switch as definedherein that connects circuit 5031 either to circuit 5036 to the primarystator windings 1260 or 5038 to at least one auxiliary or secondarystator winding disposed so that the magnetic field produced by currentin the winding lies at an angle along the circumference of the rotor,e.g., 90 degrees with respect to that produced by the primary statorwindings.

Element 5040 is a relay or actuatable switch as defined herein thatconnects the output of the generator (5036) with the electrical panelvia conductor 5014.

FIG. 5B shows a microgrid system controller 5000 in a state 5050 whereinpower from the inverter flows through switch 5016 to the subpanel alongpath 5052. In some embodiments, switch 5106 is a relay having thisposition as its quiescent state. In state 5050, the interlock 5004 is inthe position where the service switch 1010 is closed and the generatorbreaker 5002 is open. In this state, the inverter may feed power toloads on the subpanel and may further supply power to the grid. In thisstate, the apparatus of 5000 may be substantially un-powered or in alow-power standby state.

FIG. 5C shows a microgrid system controller 5000 in a state 5055 whichis the same as state 5050 except that some power flows through switches5020 and 5026 along path 5056 to charge battery 1520.

FIG. 5D shows a microgrid system controller 5000 in a state 5060, anearly step of its turn-on procedure, for example during a power outage.In this state, the interlock 5004 is in the position where the serviceswitch 1010 is open and the generator breaker may be closed. The PVinverter or inverters have shut down because of the outage. The statesof switches 5016 and 5020 isolate the regulation bus and PV inverteroutputs from the electrical panel. In this state, the battery module1520 powers an inverter circuit, such as the VFD module 1540. Thisinverter circuit may operate as a substantially fixed-frequency driverto produce an in-specification grid voltage waveform. Switches 5030 and5016 direct this voltage waveform along path 5062 to the PV inverter orinverters 1004. This state may take seconds to several minutes while thePV inverter or inverters wait for a prescribed interval of stable gridoperation before they begin to source power.

FIG. 5E shows a microgrid system controller 5000 in a state 5070 afterthe PV inverters 1004 have started to source power. In this state, theembodiment uses some of this power to charge up the mechanical energy ofthe flywheel via current flowing along path 5071 and 5072 to a devicethat rectifies the AC waveform, e.g., the battery/charge controller1520, then as a voltage having a substantial DC component along 5073 tothe VFD module 1540, then as a variable frequency and voltage waveformalong 5074 to a winding in a generator. In this embodiment, the windingis the primary generator winding. As a result of magnetically inducedtorque, the energy is transferred (5075) to rotational kinetic energy ofthe flywheel and generator. Residual power may flow to the fast dumpcircuit along path 5076.

During state 5070, the switch 5030 connects the VFD output to themotor/generator so the VFD is no longer driving the regulated bus.Instead, this bus is regulated via judicious coordination of the fastdump switch 5108, the load applied by the charge controller 1520, andthe load drawn by the VFD 1540. During this state, the regulated busmust be kept within a valid grid voltage specification or the PVinverter or inverters may stop producing power. The open switch 5040prevents the VFD output from being applied to the electrical panel.

The drive power of a single-phase motor may fluctuate at a multiple ofthe shaft rotation rate. On startup, the shaft is not spinningsynchronously with the AC output so the AC output may experience atime-varying load from the VFD. In some embodiments the VFD may modulateits drive voltage or power waveform at twice the grid-spec frequency. Insome embodiments this modulation depth may range from 0 to 1. In someembodiments, the modulation depth may change with shaft frequency.

In some embodiments, the fast dump switch 5018 modulates its load inopposition to load changes from the VFD and battery/charge controller tomaintain the regulation bus voltage within tight tolerances. In someembodiments, the charge controller may comprise a short-term storageelement like a supercapacitor or electrolytic capacitor to reduce thetime-varying load. Some embodiments may further comprise a power-factorcontrol circuit 5078 in concert with DC storage. An advantage ofpower-factor control or DC storage may be reduced flywheel spin-up timesfor a given PV inverter power.

In some embodiments, the VFD monitors the generator shaft angle forfeedback. In some embodiments, the VFD initially applies an open-loop,low-frequency and voltage current to produce an electromagnetic fieldand to induce a second magnetic field. The driven and induced magneticfields lead to a torque on the generator shaft except at node angleswhere the torque is zero. If the VFD detects that the direction ofrotation is wrong, it may reverse the sign of the applied field. It mayalternatively turn off the applied field, wait for the shaft to be in afavorable position to produce a torque in the positive direction, andapply a delayed pulse. In some embodiments, the open-loop motion controltransitions to a closed-loop control once a threshold rotation orrotation rate is established.

In some embodiments, the VFD applies a waveform having a substantiallysinusoidal base variation that is synchronous with the shaft rotationwith a prescribed phase angle relative to the shaft angle. In someembodiments, this base variation is further modulated, e.g., viamultiplication at the specified standard grid frequency.

In some embodiments, the VFD intentionally spins to a frequency that isintentionally higher than the specified grid frequency so that thegenerator can bear surge loads that occur when the electrical panel isre-powered without spinning below the specified grid frequency beforesubstantially relocking the generator output to the regulation bus andso the PV inverter can be connected to the microgrid.

In some embodiments, when the VFD reaches a target frequency, ittransitions to a mode wherein it phase locks to the waveform of theregulation bus.

Because there may be shaft angles where there is no starting torque fromthe primary winding, some embodiments further comprise an optional state5080 shown in FIG. 5F, wherein switch 5034 may re-direct VFD currentalong path 5082 to an appropriately oriented secondary or auxiliarywinding 1262. Alternatively, switch 5034 may parallel, antiparallel, orseries connect windings 1262 and 1260. The resulting magnetic fieldangle change may allow the generation of a starting torque. Once theshaft has reached a rotation amount, a target angle, or a targetrotation rate, after an interval, or some other trigger, this state mayrevert to state 5070 or state 5080 may continue through the spin up ofthe generator.

Some embodiments may switch 5034 in concert with a discrete phase changeof the VFD driving waveform. This may help to maximize the powerdelivered to the flywheel during periods where the primary phase is outof an angular position for driving the rotor/flywheel while theinstantaneous AC power is near its peak. Some embodiments may performthis switching when the frequency of rotation of the flywheel generatorapproaches that of the microgrid/inverter output.

Some embodiments may maintain a relatively high, in-specification ACfrequency in the regulated bus to the PV inverter while spinning theflywheel up to a relatively low, but in-specification generator waveformfrequency. Some embodiments may slew the AC frequency of the inverter tomatch the generator frequency and phase, then close an electricalconnection between the generator and PV inverter.

FIG. 5F shows a further actuatable switch 5084 that connects to asubstantial short circuit 5086 or low-resistance load, e.g., 10Ω-<1 mΩ.Some embodiments may close switch 5084 for a brief duration spanning azero-crossing of the AC waveform, e.g., < 1/16 of an AC cycle. Some suchembodiments may enforce the timing of at least one zero crossing of theAC voltage. Such a timed short-circuit may contribute to countering anPV-inverter-induced perturbation to check for a grid outage.

FIG. 5G shows a microgrid system controller 5000 in its operation state.After the generator and flywheel are at a target rotation frequency, theswitch 5040 may be closed, connecting the generator to the electricpanel and all loads via path 5094. In some embodiments, the resultingpower demand reduces the rotation frequency of the generator. In someembodiments, as the generator is spinning down, the fast isolator switchis closed when the instantaneous phase and frequency of the generatormatch that of the regulation bus within a tolerance, reconnecting the PVinverter to the microgrid.

In some embodiments, the deceleration of the flywheel may be activelyreduced or increased, e.g., by power from the VFD. In some embodimentsthe frequency or phase of the regulated bus may be adjusted by changinga target waveform in a control loop or by increasing or reducing one ormore applied loads to minimize or reduce the instantaneous or predictederror in the phase and frequency between the regulated bus and generatorwaveform e.g., to facilitate a smooth and rapid transition to amicrogrid in stable equilibrium.

This mode maintains the regulation bus within a grid specificationwaveform by actuation of one or more of switches 5020, 5022, 5026, and5018. The generator efficiency, power factor, and frequency may beadjusted via the variable frequency drive and switch 5034. The VFD canalso provide additional power to the subpanel via the generator withswitch 5030 in the indicated position. The VFD can provide directsupport for the regulation bus and inverter even when the PV inverter isisolated by switch 5020 by switching 5030 to the regulation-busposition.

In some embodiments one or more of switches 5016, 5018, 5020, 5022,5026, 5030, 5034 may be controlled by the agent controller as disclosedherein. In some embodiments, one or more switches may be controlled bythe VFD controller. In some embodiments, one or more switches may becontrolled by a third controller. Some embodiments comprise a controllerthat can actuate one or more relays. Some embodiments comprise arelay-actuating controller that can further reduce the relay-drivevoltage while relay states are not changing to reduce heating and powerdraw.

Some embodiments alternatively comprise a multiple-phase VFD controllerhaving a second output 5096 that may drive a secondary stator windingdirectly. Some embodiments further comprise a direct connection 5098 ofa first output to a primary stator winding, some in lieu of switch 5034.Some embodiments may comprise a third VFD output to a third statorwinding. Some embodiments may comprise additional outputs to additionalwindings. Some embodiments may comprise a capacitor across the secondarystator winding as known in the art.

Some embodiments may drive a plurality of windings in a least oneoperating state such that the total power drawn power is substantiallyconstant. Some embodiments may drive at least one winding with asubstantially sinusoidal output and a second winding with aphase-shifted, substantially sinusoidal output. Some embodiments maydrive a second winding with a second waveform that is adjustedstatically or dynamically to improve the generator outputcharacteristics, e.g., sinusoidality, noise, apparent source resistance,etc.

Some embodiments may operate in a system that comprises a connection toan energized grid 1005 and optionally an AC-side battery/inverter system6002 and optionally a PV inverter 1004 as shown in FIG. 6A. In such asystem, the controller will phase lock to the grid, and may not actuateits fast dump switch 5108.

Some embodiments may operate in a system such as 6100 in FIG. 6B, thatis disconnected from an electrical grid and comprises an externalislanding or microgrid system controller, such as AC-sidebattery/inverter system 6002, and may further comprise a PV inverter1004. In such a system the controller may phase lock to the voltagewaveform produced by the external microgrid system controller. In such asystem, the generator may provide surge power (6102) and in someembodiments, reactive power mitigation that reduces the surge power(6104) capacity required of the battery/inverter.

Some embodiments may operate in a grid-tied or islanding system such as6200 in FIG. 6C, comprising one or more of a hybrid inverter 6202, aDC-fed battery/inverter 6204, a DC-side battery storage system 6206, anda PV inverter. When connected to an energized grid, some embodiments mayidle, charge its batteries, or operate normally, phase locked to thegrid waveform, to buffer and stabilize power. When disconnected from thegrid, some embodiments may phase lock to an external microgrid systemcontroller or islanding inverter if one is present, otherwise it mayoperate as the microgrid system controller. In some embodiments thisoperating behavior is configured manually. In some embodiments, thesystem automatically detects the presence of another controller based ona waveform, wired or wireless signal, user input, or the like.

Some embodiments, such as 7000 in FIG. 7, may be powered directly (7002)from the PV system without an external PV inverter. Some embodimentsfurther comprise a power optimizer/rapid shutdown device 7003, such as a‘balancer.’ Some balancers further comprise DC-side battery storage.Some such embodiments comprise a single-phase VFD such as 1540 to startup and maintain the rotation of a single-phase generator (1200). Theembodiment shown in FIG. 7 comprises a three-phase inverter 7004 thatdrives a three-phase motor 7006, to establish and maintain rotation ofthe rotor of generator 1200. This may have the advantage of reducingstorage capacitance requirements and drive power pulsations. Someembodiments may alternatively or in addition comprise an additionalelement 7008 that can drive generator and flywheel rotation, e.g., via alinkage 7010. Some such embodiments may comprise an electric motor or aheat engine. Some embodiments may further comprise a converter 7012 thatproduces a storable energy source for 7008 from substantially DC power,such as a hydrolysis system. Some embodiments may comprise a refillableenergy source, such as a fuel tank 7014.

Some embodiments such as 8000 in FIG. 8 are employed in a three-phaseelectrical system and use a three-phase generator 8002. Some suchembodiments derive power from an external inverter like the embodiment5000. The embodiment 8000 draws DC power directly from one or more solarpanels. Some embodiments further comprise one or more of: an integratedrapid shutdown device, PV power optimizer, or DC-side battery storage(e.g. 7003).

Some embodiments such as 9000 in FIG. 9 are employed in a single-phaseelectrical system and use single-phase generator (1200) and comprise aDC-side battery storage, PV power optimizer, and rapid shutdown module7003 for internal power instead of 1520.

The following embodiment is described at least partially with to FIG.1A:

-   -   A microgrid system controller for creating and maintaining a        microgrid, the microgrid electrically coupled to an inverter        associated with an energy supply, comprising:    -   an inertial power module having a motor/generator and a flywheel        assembly;    -   a source control module having a first controller, a battery        bank module, and at least one bridge circuit, wherein the first        controller is configured to monitor a first line associated with        a microgrid and a second line associated with the        motor/generator, and based on a status of at least one of the        first line or the second line, the first controller is        configured to:        -   provide first control signals to a first actuatable switch            to connect and disconnect an output of the motor/generator            with the microgrid, and        -   provide second control signals to a second actuatable switch            to connect and disconnect output from the inverter with the            output of the motor/generator,    -   and wherein the at least one bridge circuit is coupled to the        battery bank module and configured to provide energy from the        battery bank module to drive the motor/generator and the        flywheel assembly; and    -   a load control module having a second controller, at least one        actuatable switch, and a line load, wherein the second        controller is configured to monitor the first line associated        with the microgrid, and based on a status of the first line, the        second controller is configured to provide third control signals        to the at least one actuatable switch to provide energy to the        line load.

The following embodiment is described at least partially with regard toFIG. 1B:

-   -   A microgrid system controller for creating and maintaining a        microgrid, the microgrid electrically coupled to an inverter        associated with an energy supply, comprising:    -   a motor/generator and a flywheel assembly;    -   a battery bank module;    -   at least one bridge circuit;    -   a line load; and    -   a controller, wherein the controller is configured to sense a        first line parameter from the inverter and a second line        parameter from the motor/generator, and based on a status of at        least one of the first line parameter or the second line        parameter, the first controller is configured to:        -   provide first control signals to a first actuatable switch            to connect and disconnect the inverter with the            motor/generator,        -   provide second control signals to a second actuatable switch            to connect and disconnect the microgrid with the line load,            and        -   provide third control signals to a third actuatable switch            to connect and disconnect the motor/generator with the            microgrid,    -   and wherein the at least one bridge circuit is coupled to the        battery bank module and configured to provide energy from the        battery bank module to drive the motor/generator and the        flywheel assembly.

The following embodiment is described at least partially with regard toFIG. 1C:

-   -   A microgrid system controller for creating and maintaining a        microgrid, the microgrid electrically coupled to an inverter        associated with an energy supply, comprising:    -   a motor/generator and a flywheel assembly;    -   a battery bank module;    -   at least one bridge circuit;    -   a line load; and    -   a controller, wherein the controller is configured to sense a        first line parameter from the inverter and a second line        parameter from the motor/generator, and based on a status of at        least one of the first line parameter or the second line        parameter, the first controller is configured to:        -   provide first control signals to a starter switch to connect            and disconnect the inverter with the motor/generator,        -   provide the first control signals to the starter switch to            connect the inverter with the motor/generator during a first            time period when the first line parameter is below a            predetermined threshold,        -   provide the first control signals to the starter switch to            connect the inverter with the microgrid during a second time            period when the first line parameter exceeds a predetermined            threshold,        -   provide second control signals to a second actuatable switch            to connect and disconnect the microgrid with the line load,            and        -   provide third control signals to a third actuatable switch            to connect and disconnect the motor/generator with the            microgrid,    -   and wherein the at least one bridge circuit is coupled to the        battery bank module and configured to provide energy from the        battery bank module to drive the motor/generator and the        flywheel assembly.

Specific details are given in the description to provide a thoroughunderstanding of exemplary configurations including implementations.However, configurations may be practiced without these specific details.For example, well-known circuits, processes, algorithms, structures, andtechniques have been shown without unnecessary detail in order to avoidobscuring the configurations. This description provides exampleconfigurations only, and does not limit the scope, applicability, orconfigurations of the claims. Rather, the preceding description of theconfigurations will provide those skilled in the art with an enablingdescription for implementing described techniques. Various changes maybe made in the function and arrangement of elements without departingfrom the spirit or scope of the disclosure.

While various examples have been provided in the specification anddrawings, it should be apparent to those skilled in the art that thescope of the disclosure is not limited to the specific embodimentsdescribed herein. For example, features of one or more embodiments maybe combined with one or more features of other embodiments withoutdeparting from the scope of the disclosure. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense. Thus, the scope of the disclosure should bedetermined not with reference to the above description, but withreference to the appended claims along with their full scope ofequivalents.

What is claimed is:
 1. A microgrid system controller, comprising: aregulated bus; a battery and charge controller switchably coupled to theregulated bus; a variable-frequency drive (VFD) inverter coupled to thebattery and charge controller; a generator physically coupled to arotatable flywheel and switchably coupled to the VFD inverter; aresistive load switchably coupled to the regulated bus; and a pluralityof actuatable switches, wherein the plurality of actuatable switchescomprise: a first actuatable switch configured to selectively couple aphotovoltaic (PV) inverter to the regulated bus or to an externalelectrical panel; a second actuatable switch configured to selectivelycouple the regulated bus to the external electrical panel; a thirdactuatable switch configured to selectively couple the regulated bus tothe battery and charge controller; a fourth actuatable switch configuredto selectively couple the VFD inverter to the regulated bus or to thegenerator; a fifth actuatable switch configured to selectively couplethe generator to the external electrical panel; and a sixth actuatableswitch configured to selectively couple the resistive load to theregulated bus.
 2. The microgrid system controller of claim 1, whereinthe plurality of actuatable switches comprise a seventh actuatableswitch configured to selectively couple a user-configurable load to theregulated bus.
 3. The microgrid system controller of claim 1, whereinduring a first state power from the PV inverter is supplied to theexternal electrical panel, and the plurality of actuatable switches areconfigured such that: the first actuatable switch couples the PVinverter to the external electrical panel; the fourth actuatable switchcouples the VFD inverter to the regulated bus; and the sixth actuatableswitch is open so that the resistive load is not coupled to theregulated bus.
 4. The microgrid system controller of claim 1, whereinduring a second state power from the PV inverter is supplied to theexternal electrical panel and to the regulated bus, and the plurality ofactuatable switches are configured such that: the first actuatableswitch couples the PV inverter to the external electrical panel; thesecond actuatable switch couples the regulated bus to the PV inverter; athird actuatable switch couples the regulated bus to the battery andcharge controller to charge a battery; the fourth actuatable switchcouples the VFD inverter to the regulated bus; and the sixth actuatableswitch is open so that the resistive load is not coupled to theregulated bus.
 5. The microgrid system controller of claim 1, whereinduring a third state the VFD inverter provides an in-specification gridvoltage waveform to the PV inverter, and the plurality of actuatableswitches are configured such that: the first actuatable switch couplesthe PV inverter to the regulated bus; the second actuatable switch isopen so that the regulated bus is not coupled to the external electricalpanel; the fourth actuatable switch couples the VFD inverter to theregulated bus, wherein a battery coupled to the battery and chargecontroller is configured to power the VFD inverter, and the VFD inverteris configured to provide the in-specification grid voltage waveform tothe PV inverter; and the sixth actuatable switch is open so that theresistive load is not coupled to the regulated bus.
 6. The microgridsystem controller of claim 1, wherein during a fourth state power fromthe PV inverter is supplied to the generator to charge up mechanicalenergy of the rotatable flywheel, and the plurality of actuatableswitches are configured such that: the first actuatable switch couplesthe PV inverter to the regulated bus; the second actuatable switch isopen so that the regulated bus is not coupled to the external electricalpanel; the third actuatable switch couples the regulated bus to thebattery and charge controller, and the battery and charge controllerpower the VFD inverter; the fourth actuatable switch couples the VFDinverter to a primary winding of the generator, wherein the VFD inverteris configured to provide a variable frequency and voltage waveform tothe generator to charge up the mechanical energy of the rotatableflywheel; the fifth actuatable switch is open so that the generator isnot coupled to the external electrical panel; and the sixth actuatableswitch is controlled to maintain the regulated bus within a grid voltagespecification waveform by providing residual power from the PV inverterto the resistive load.
 7. The microgrid system controller of claim 6,wherein during a fifth state the fourth actuatable switch couples theVFD inverter to a secondary or auxiliary winding of the generator. 8.The microgrid system controller of claim 1, further comprising a seventhactuatable switch configured to selectively couple the regulated bus toa substantial short circuit.
 9. The microgrid system controller of claim1, wherein during a sixth state power from the generator and rotatableflywheel is supplied to the external electrical panel, and the pluralityof actuatable switches are configured such that: the first actuatableswitch couples the PV inverter to the regulated bus; the secondactuatable switch, the third actuatable switch, and the sixth actuatableswitch are controlled to maintain the regulated bus within a gridvoltage specification waveform; the fourth actuatable switch iscontrolled to adjust generator efficiency, power factor, and frequency;and the fifth actuatable switch is closed to couple the generator to theexternal electrical panel.
 10. The microgrid system controller of claim1, wherein the external electrical panel is coupled to an energizedgrid, and a waveform of the VFD inverter phase locks with a waveform ofthe energized grid.
 11. The microgrid system controller of claim 1,wherein the external electrical panel is coupled to a battery/invertersystem, and a waveform of the VFD inverter phase locks with a waveformof the battery/inverter system.
 12. The microgrid system controller ofclaim 1, wherein the PV inverter is coupled to a battery/inverter and abattery storage system, and a waveform of the VFD inverter phase lockswith a waveform of an islanding inverter.
 13. A microgrid systemcontroller, comprising: a regulated bus; a battery and charge controllerswitchably coupled to the regulated bus; a multiple-phasevariable-frequency drive (VFD) inverter coupled to the battery andcharge controller; a generator physically coupled to a rotatableflywheel and electrically coupled to the multiple-phase VFD inverter,wherein an output of the multiple-phase VFD inverter drives at least oneof (i) a primary stator winding of the generator, or (i) a secondarystator winding of the generator; a resistive load switchably coupled tothe regulated bus; and a plurality of actuatable switches, wherein theplurality of actuatable switches comprise: a first actuatable switchconfigured to selectively couple a photovoltaic (PV) inverter to theregulated bus or to an external electrical panel; a second actuatableswitch configured to selectively couple the regulated bus to theexternal electrical panel; a third actuatable switch configured toselectively couple the regulated bus to the battery and chargecontroller; a fourth actuatable switch configured to selectively couplethe generator to the external electrical panel; and a fifth actuatableswitch configured to selectively couple the resistive load to theregulated bus.
 14. A microgrid system controller, comprising: aregulated bus; a balancer comprising battery storage, the balancercoupled to an output of a photovoltaic (PV) system and coupled to theregulated bus; a battery and charge controller switchably coupled to theregulated bus; a variable-frequency drive (VFD) inverter coupled to thebattery and charge controller and switchably coupled to the regulatedbus; a generator physically coupled to a rotatable flywheel and a motorelectrically coupled to the VFD inverter, the generator switchablycoupled to an external electrical panel; a resistive load switchablycoupled to the regulated bus; and a plurality of actuatable switches,wherein the plurality of actuatable switches comprise: a firstactuatable switch configured to selectively couple the regulated bus tothe VFD inverter; a second actuatable switch configured to selectivelycouple the regulated bus to the battery and charge controller; a thirdactuatable switch configured to selectively couple the generator to anexternal electrical panel; and a fourth actuatable switch configured toselectively couple the resistive load to the regulated bus.
 15. Themicrogrid system controller of claim 14, wherein the balancer comprisesdirect current (DC) side battery storage.
 16. The microgrid systemcontroller of claim 14, wherein the VFD inverter is a multi-phase VFD,the motor is a multi-phase motor, and the generator is a single-phasegenerator.
 17. The microgrid system controller of claim 14, furthercomprising: a converter switchably coupled to the regulated bus, whereinthe converter is configured to produce a storable energy source fromdirect current (DC) power; and a motor coupled to the converter and tothe generator, the motor configured to drive the generator and rotatableflywheel.
 18. A microgrid system controller, comprising: a regulated buscoupled to an output of a photovoltaic (PV) system; a battery and chargecontroller switchably coupled to the regulated bus; a multi-phasevariable-frequency drive (VFD) inverter coupled to the battery andcharge controller and switchably coupled to the regulated bus; amulti-phase generator physically coupled to a rotatable flywheel andcoupled to the multi-phase VFD inverter, the multi-phase generatorswitchably coupled to an external electrical panel; a resistive loadswitchably coupled to the regulated bus; and a plurality of actuatableswitches, wherein the plurality of actuatable switches comprise: a firstactuatable switch configured to selectively couple the regulated bus tothe multi-phase VFD inverter; a second actuatable switch configured toselectively couple the regulated bus to the battery and chargecontroller; a third actuatable switch configured to selectively couplethe multi-phase generator to the external electrical panel; and a fourthactuatable switch configured to selectively couple the resistive load tothe regulated bus.
 19. The microgrid system controller of claim 18,wherein the multi-phase VFD inverter is a three-phase VFD inverter andthe multi-phase generator is a three-phase generator.
 20. A microgridsystem controller, comprising: a battery storage device coupled anoutput of a photovoltaic (PV) system; a regulated bus coupled to thebattery storage device coupled; a variable-frequency drive (VFD)inverter switchably coupled to the regulated bus; a generator physicallycoupled to a rotatable flywheel and coupled to the VFD inverter, thegenerator switchably coupled to an external electrical panel; aresistive load switchably coupled to the regulated bus; and a pluralityof actuatable switches, wherein the plurality of actuatable switchescomprise: a first actuatable switch configured to selectively couple theregulated bus to the VFD inverter; a second actuatable switch configuredto selectively couple the generator to the external electrical panel;and a third actuatable switch configured to selectively couple theresistive load to the regulated bus.